Hetfinch...I suffered badly early in 2003 and ended up starting but not finishing at London...gutted.
Anyway, for a few months I felt crap and was advised only to exercise gently but "not too tiredness"...I then had acupuncture and a homeoptahic consultation (potions in water for weeks!) and remedial massage. So, no control as to what worked the best but my money would be on the acupuncture.
I would say though that I'm still not 100% and can't do the training I used to but it's bearable (well sort of). Some days I wonder if it's all in my head and I'm just not as fit, or older, or have lost the mental toughness I used to have...but then I change my mind and think I'm still not over it. My physio reckons these virus things never actually fully clear up but lie dormant and can still affect you years down the line, especially when tired or run down.
SO, that's not hugely encouraging is it?! But, I ran a marathon in October and will run London in April plus maybe a trail ultra in the summer...just slower than I used to and with longer recovery after.
Hope this helps? Amanda