I can't breathe. My face is almost completely under the water. In my mind I'm gliding effortlessly, with my head relaxed and in perfect alignment with my spine, but I suspect that's the lack of oxygen talking.
In fact I can see the reality in front of me. There's a mirror directly below me on the bottom of the pool and not only am I flapping around like a drowning man, but my face is turning a troubling shade of puce.
Obviously I could, and should, just turn my head on the next stroke and take some air but I'm focusing so hard on trying to keep my head down and my body flat that I keep forgetting. In any case the last time I tried it I caught a mouthful of water and I'm anxious not to repeat the experience. If they ever introduce a triathlon race distance with a 25-metre swim leg I'll be fine; anything longer and I'm screwed.
Three hours earlier I was breathing without a problem. My swimming was still atrocious but I could breathe. Now I can't breathe and I can't swim, but, strangely enough, that's progress.
At least now I can clearly understand that trying to breathe while swimming with my head mostly out of the water is counterproductive. It forces my hips down and my chest up; much of the effort of my arms and legs is then focused on trying to correct that rather than propelling me forward. The result is that instead of trying to slip through the smallest possible hole in the water, it feels like I'm trying to push a barn door in front of me while I'm swimming.
I've heard all this before. I'm two months along the path of trying to turn myself into a decent swimmer - or at least one good enough to stay with the pack in the swim leg of a triathlon - and everyone who's had a look at my front crawl so far has reached the same conclusion: rubbish. The difference this time is that I can see it, too.
An hour earlier I was reviewing my pitiful attempt at freestyle from every conceivable angle on a large video screen suspended above the end of the pool. Although it's mildly embarrassing watching yourself thrashing about on a big screen, it's incredibly useful to see instantly what you're doing wrong before you think about correcting it.
The water shed
This is my first experience of swimming in an Endless Pool - a small swimming tank with a variable current that holds you in place like an aquatic version of running on a treadmill - and of video feedback. While neither is now a unique experience in the world of triathlon, the analysis, critique and correction of my swimming that follows it certainly is, as is the location.
SwimShack, the swim studio where I'm being put through my strokes in a one-to-one workshop, is housed in the garden shed of an innocuous suburban house on the outskirts of Loughborough. It's the home of Ian Smith, the head coach of Total Immersion Swimming UK, which employs a revolutionary, if controversial, approach to teaching you how to swim more effectively.
"Our mission is to help people become the best swimmer they can be, whether that's someone learning to swim for the first time as an adult or that tiny percentage of people who are elite, age-group or competitive swimmers," says Smith, who looks a little like an old-school drill instructor but talks with the passion and belief of a religious convert. "It's a programme that will work for anyone who wants to improve their swimming."
The promise of Total Immersion Swimming, which was first developed as a programme in 1989 by American swim coach Terry Laughlin, is simple but grand: to help you swim better, faster and easier. The road to that goal is the same for everyone.
There's no tinkering with your existing stroke - everyone starts again from scratch with a number of basics drills and movement patterns that are designed to re-educate your body to move more easily through the water. It's that focus on swimming more easily that resonates so strongly with triathletes.
Of course we all want to be faster swimmers, but not at any cost. It's more important to exit the water with enough energy in the tank to do yourself justice on the bike and running legs.
You can reach that goal if you learn to swim more like a fish. That doesn't mean extracting oxygen from water rather than air, it means understanding the importance of flow and learning the skills of balance, slippery body positions and core-based fluent movements.
Strokes of genius
Although those might seem like quirky, offbeat ideas they are exactly what some of the world's finest swimmers practise and perfect through hours in the water.
When Laughlin studied swimmers like multiple Olympic champion Ian Thorpe and the great Russian sprinter Alexander Popov he noticed that their languid movements belied their remarkable speed.Watch almost any significant swimming competition and you'll notice the same thing. The fastest swimmers will almost certainly be those taking the fewest strokes.
That's not because they are putting more power into their strokes - most club triathletes would outperform an elite swimmer in tests of raw strength and power - it's because each of their strokes is longer or, more importantly, their body travels further with each stroke.
In practical terms the Total Immersion programme is trying to replicate the same thing: a body position that minimises drag and a clean, simple stroke that, by engaging the whole body, seems effortless in the water.
Most people learn the basics of such a stroke at one of Total Immersion's two-day weekend workshops that take place all over the UK throughout the year. I'm trying to squeeze a truncated version of the programme into three sessions in a single day, which makes my first real lesson at the school of fishlike swimming a test of my natural impatience. I have to lie on my back without sinking. Like balancing on a bike for the first time as a child, it's initially frustratingly difficult, but natural and instinctive when you know how to do it.
The concept of balance in the water is one of the revelatory cornerstones of the Total Immersion programme. We think we are doing it but we aren't; yet you can't move forward, literally or figuratively, without it.
Balance keeps you horizontal in the water, frees your arms and legs to lengthen your stroke, and liberates your power. Lengthening is the most important function of the arms in freestyle swimming.
"It doesn't matter what programme you are following, there are no long-term quick fixes with swimming," says Smith, sensing my frustration at my inability to stop myself sinking. "We talk about having to do 20,000 repetitions of a movement to make it permanent and instinctive, but when you are trying to break down an ingrained poor movement pattern, it's more like 100,000 repetitions."
So I suppose I should be encouraged by the fact that it only took me 20 minutes to learn to lie flat on my back without sinking and that I mastered kicking from my buttocks almost immediately. My difficulties started when I had to roll onto my side with my face in the water and try a drill called skating.
The point of the drill is to teach you how balance should feel when you start swimming and it should also help you to breathe by conditioning you to roll your body to where the air is. It was a struggle - I could keep my body balanced with my head down but I just couldn't manage to breathe properly.
I wasn't releasing air into the water, which was creating tension throughout my body, and instead of gently rolling over onto my side to catch some air with one fluid movement I was either making sudden manic gasp for air or trying to see how long I could last without breathing at all.
As soon as I felt I was making some progress with breathing - the futility of not breathing when you have your head under the water is not something you repeat too many times - everything else fell apart. I wasn't kicking properly, my hips started to drop and my balance disappeared.
"Change takes time. Swimming is no different from any movement-based activity you would do on dry land," says Smith, who is in the pool beside me physically trying to move me to the correct position or adding a real-time commentary to the video footage for a personal DVD that I can take away and watch later.
"The whole is the sum of a number of small, integrated movement patterns. Each might in itself be simple but you have to learn one before you can move on to the next. No one does everything well the first time, there's always something that is a problem, whether it's kicking, breathing or using your arms to lengthen."
I'd like to say that after five hours in the water with individual tuition and video analysis I had developed a stroke that would power me up and down my local pool with effortless grace. Unfortunately, I hadn't and my day at SwimShack ended with more confusion than certainty about what I was supposed to be doing. My head was swamped, as were my lungs.
It wasn't until later that week, when I went to the pool to practise the skill of swimming rather than to train, that I realised I'd absorbed the message of the programme. Trying to be a better swimmer starts in your head, if you are prepared to think about what you're doing with every movement in the water.
I'm a long way from being a good swimmer but my drills have progressed to the point where
my arms are now working in unison along two imaginary rails that I'm trying to swim beside.
From the outside it actually looks like front crawl and it must be more efficient because my stroke count is down from an average of 25 strokes to 23. I doubt very much that it will worry Michael Phelps but it is progress. What's more, I can now breathe.