I think it may depend on how strenuous the exercise is rather than the duration, but I have a similar observation. I normally sleep 6-6.5 hours at night. When I

I think it may depend on how strenuous the exercise is rather than the duration, but I have a similar observation. I normally sleep 6-6.5 hours at night. When I did p90x (45-60 minute sessions) a few years back, I would usually be wide awake after 5 hours. I suspect this is because I sleep really deeply when tired - I remember most of those nights sleeping dreamlessly.