It's not always an hour of fatigue transfered.
More testing is needed. Last time I casted it took 12 mins. of fatigue and gave 2 mins. of sleep bonus.
I've not really checked the fatigue cost though I did think it was approximately half an hour. Looking at the full page and what you state above it could be you get 1 minute of sleep bonus for each six minutes of fatigue so ten minutes of sleep bonus would then cost the full hour mentioned.
--[[User:Gaeron|Gaeron]] 09:25, 9 August 2011 (UTC)