Selena asks: After my long runs, I can barely stay awake. When I get home, I fall asleep for at least four hours. I am usually very sore and stiff when I do wake up, since I hadn't been moving. So my whole Saturday is ruined because all I want to do is sleep. I feel like I hydrate well. I thought that when you run or work out you make all these happy stimulating endorphins that give you a lot of energy? Why am I lacking that, and what can I do to fix it?
Fatigue after exercise, especially long duration or high intensity, is not unusual. However your sleepiness seems beyond the normal level of fatigue that runners experience on a routine basis. You could be on the far end of the normal spectrum or there could be an underlying problem. Running affects each person individually and the response can vary from the endorphin high that you are seeking to varying levels of fatigue. It sounds like you are paying attention to hydration and energy supplementation. The weekend timing is interesting; I wonder about cumulative fatigue from a long week and if it plays a role.
Your age, sleep habits, nutrition and energy balance, blood counts, thyroid status, menstrual status, number of children at home, work and life stresses all could play a role in your need to sleep after long runs. Sitting down with your GP and working through your story along with some physical examinations and tests would be your best bet for finding an answer to your question.
My first guess without any of the additional information noted above based on the Saturday timing is that you are not getting enough sleep during the week. That is very common among adults and teens, probably a result of trying to do too much and not leaving enough time for sleep. In my practice, most people are an hour or two (or more) short on daily sleep. The first intervention you might try on your own is moving your bedtime 20 minutes earlier each week until you are getting an hour or two of more sleep each night to see if that will reduce your post-run sleepiness.
If you are running for fitness, you probably do not need the long run and sticking with 30 to 60 minutes of running most days of the week will allow you to maintain the health benefits of regular exercise. If you are not racing or training for a long distance event, three to five miles a day three to five times a week should be adequate for your long term health, especially if you add in some strength training.