I need help. I am having shorter and shorter LDs every time I have them for what I think is one reason alone. I expect them to end soon. They do not start to fade out until I rmeember to do a prolonging technique. But I cannot control myself from trying to prevent them because I expect them to end. So I need some advice. What are some techniques I can use to get rid of these expectations. Its not as easy as it may sound. Its an association that my brain has made that I hope i can get out of somehow: the association is that every time I am lucid it will end soon. What should I do?
Try self-hypnosis! (other threads are around for this, use Search)
Tip: In self-hypnosis, say that you will use self-hypnosis again. It might help (you can’t really tell)
I’ve had this problem too for about a year. Nowadays it’s better but sometimes it comes back. I’ve solved it by ignoring it. It ain’t easy… but try not to think about it… Instead, think about the joy, freedom and endless possibilities of the dream. Don’t see the glass as half empty, but convince your mind that it’s half full… It may not help you after one, two or ten times… but you have to hold on. Perhaps you can combine it with self suggestion and self hypnosis. For instance, you could repeat a mantra while falling asleep in the evening… something like “When I WILL become lucid, I won’t wake up too soon” or alike. I’m not sure whether or not it might help, but you could experiment with different mantras or other techniques. In any case, don’t expect major improvements too soon. You have to make a shift in your subconscious thinking and this always takes time.
Good luck! 
When I first started to LD I would realize I am dreaming and there would be so many things I wanted to try and I knew that my time in the LD was limited. ( Every LD does have to come to an end at some point. ) So I would start to do everything I wanted to try almost at once going from one thing to another. The result was that I could never really enjoy one experience. I was acting like this was going to be my last LD. What I did was change how I think. As I had more LD ‘s I knew I would have more and I did not have to rush through the dream. I was then really able to explore my dreams and really enjoy every experience.
I know it is not the same as what you are going through but, the cure might be the same. Instead of worrying about the dream ending just worry about immersing yourself in the experience. You will wake up but that’s ok because the dream world will always be there and you will be visiting it again.
Happy Dreaming
Forget about the prolonging technique for a while and focus on what you would do if you already had longer LD:s.