sleeps important, worth getting sorted.
regular rhythms obviously helps, but i know what you mean, playing at night kinda messes this up, but theres plenty you can do to mitigate the problem.

you dont sleep well if you brain is still highly active (like after playing poker), you need to relax into your body, ie let your blood/energy drain out your head, so youve got normal blood flows again.

hot baths, or just getting your feet in hot water helps.
feeling you feet, rotating you ankles 100 times one way 100 times the other b4 sleep helps get your attention back into the body.
u can learn some meditation, relaxation techniques, tai chi etc. The Chinese (Tai chi/chi gung people) know a lot of good stuff about these things, (useful at the table too [img]/images/graemlins/wink.gif[/img] )

While your're playing - How relaxed are you, how aware of your body are you, use the breaks to relax - release the stress at the time.
For anything the sooner you release stress the easier it is, if you leave it too long its like concrete after its set. it drains you long term and sets into the body, you go numb to it.

I've hardly read anywhere in poker books about the importance of relaxation. The top players talk about feel - but what helps you to feel - relaxing!!
Instinct, feel these things have a lot to do with the body. - play with your mind and body.

I dont know if this helps,
anyway, hope you find some way to sleep better