Caleb's_Syde that might work for you, but for many people the reason why they can't sleep on acid is not because of their breathing, it's because they can't clear their minds and stop thinking so much!
I've often gone to bed thinking that my trip is over, tried to sleep but couldn't because my mind was still too active, all I could do was self evaluate my life and think bullshit.
The controlled breathing idea does work sometimes, I actually tried doing it the other night, and even though it took me 4 hours to sleep, my body was quite relaxed.
Once again, smoke the weed and you shouldn't have too much trouble sleeping... unless you've dropped a few too many tabs in the first place ;D
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*madhuGz*