I never heard my hypnobirthing CD start to finish and it completely worked for me (with all 4 babies, no drugs any time because it just didn't ever hurt that much), so don't worry about falling asleep. If you want to then perhaps try another go listening in the middle of the day, but sitting in a comfy chair instead of lying in bed and you may stay more awake.

Also print out your birthing affirmations and pin them around your house (fridge, bathroom, etc) so you will be exposed to them all the time. And keep reading your book, make sure the knowledge you are gaining is as deep into your sub conscience as possible.

Good luck and enjoy your upcoming labour

T
xx