I really sympathise, misschief. Both my pregnancies involved large amounts of burning vomit in the back of the throat 24/7 ie heartburn (and virtually from the day of conception too!), so sleep was difficult to say the least. Am also a bit of an insomniac on top of it all. Both my labours were extremely long - 3 days and 2 days (mostly at night so no sleep to speak of). BUT you can do it. Honest you can. It is exhausting but I produced two healthy babies at the end of it.
I can give you some of my tips for insomnia if you like, but my ultimate message is that although you FEEL you can't go on and panic about how little sleep you're getting (god, do I know that feeling) it really is surprising how little sleep you can function on. Really. Trick is not to worry about it. Easier said than done, I know, but I read somewhere that 85% of insomnia is caused by people worrying about not sleeping. If you can try not to worry, and tell yourself daily how well, comparitively, you are functioning on the little sleep you do get, hopefully you can feel less panicky about the whole thing and the vicious circle will be broken?
Anyway - top tips.
If you are worrying about something in the night (probably about how little sleep you're getting),imagine the worry is on a CD. Take it off, put it in its case and put another one on - the CD of the last good holiday / party / night out you went on. Thinking about something else will help you switch off.
Tell yourself that if you are not asleep in 10 mins, you are going to get up. Get up, take a blanket and go and lie on your sofa (or the spare bed if you have one). Changing where you sleep helps - I often get a few hours on the sofa when I have insomnia, and I usually fall asleep on it in minutes!
If all else fails, go through, scene by scene, your favourite film, book, television series - or even something you have just seen/read. You have to play it in your head as it actually happens ie try and remember all the details of the dialogue, the scenery, what the characters wear and what they do. If you forget a scene, rewind back to where it comes in and play the whole thing back again. This gets your mind concentrating on something else other than what is keeping you awake and before you know it, you are asleep!
Anyway, hope that helps. Just remember, whatever happens, you can do it. Buy some glucose sweets for the labour - they help (psychologically if nothing else) when you feel like you are flagging. Good luck!