I notice after a hard session i find it hard to sleep. My body is still 'tingling', and my head too alert or thinking too much.
I know for many a good work out means a good night's sleep, though seems to be the reverse for me.
It's annoying, though might be exasperated by me doing them in the evening, finishing at 7.15pm, the 30 mins walk home. But that can't really be changed, as it circuits class, and due to work commitments.