Another sleep study

Tonight is my 2nd sleep study.  The first one was ok but I couldn't really fall asleep.  I think I only slept like 4 hours.  So they wanted me to come in for another one.  This time I think they will put the CPAP on and see how it goes.  I should be able to fall asleep fairly quickly because I have slept 3 hours in the last 38 hours.  So I think I should be ok.  But right now, 6 hours before the study, I feel pretty awake.