hi there tuner,
i too suffered from 'student disease', too much booze, too many drugs and late nights, too much bad food, too much playstation, also too much sitting reading and writing too....obviously!
i know nothing about cracking necks and stuff. sounds like you must be sleeping awkwardly or something...have you tried changing your pillow? or using an extra pillow? or perhaps you need to use one less pillow? or something....sorry...
as far as your ass goes, i know what you mean! i don't get fat there, i got it around my belly, but everyone has a place where they store their fat. all i can suggest is that you should start you exercise and diet routine, work it into your life and stick to it. the places where the fat gathered last will loose first (as far as i can tell from myself) and the places you gained first you will loose last. so it depends on where your ass was on the 'gaining timetable' where it will be on the 'losing timetable.'
exercising certain areas does build muscle there but only through losing fat, and that means cardio, can you really reduce the size of it. see my belly for a perfect example! i do loads of ab exercises and the muscles are there now, it is just that they are under the fat! well there is not that much fat there now, i can just, just pinch about 1/2 an inch...anyway it'll be the same for your ass. exercise away, do calf raises, prone leg curls, lunges, etc and you will build muscle but you're going to have to burn the fat off too!
good luck!