Why you - You've said it yourself - you've always been a worrier.
It didn't happen in college because you could focus your worries onto college studies, etc. It didn't happen when you moved out of your parents house because you could focus your worries on moving out, etc. but you still will have worried - it is just that your worries would have be contained to the situations you found yourself in and so they made perfect sense - your worries were validated because of the situations you found yourself in.
So like you say you've trained yourself to be a worrier, but before when you worried it was for good reason (or at least in your mind it was for good reason), you had a exams to prep for, a house move to plan, etc., etc.
The trouble is NOW you're an expert worrier but your mind has nothing "sensible" to worry about IE: normal stuff, that everyone worries about (and this is where we all develop the skill!!), but it has been trained to worry and is now STUCK in the HABIT. And it is because of that, because that's what you've had it doing for years, that it is still looking for stuff to worry about, because that's been it's job - FOR YEARS.
How many times will you have laid in bed in the past worrying about exams, moving house, etc.??? Well you mind has just got used to worrying when you lie in bed (or whenever else you have time on your hands with nothing to do but THINK) and so it is doing just what it has always done.
So that's why you. You've developed the skill for it and now you have nothing "sensible" to worry about, to focus on, your mind is just finding "stuff" instead and this "stuff" can be anything - literally ANYTHING (and why some of it can be so hard to comprehend - as a lot of it doesn't even make sense
So all you've got to do is break that worrying habit and re-train your mind, tell it that lying in bed doesn't mean worry time, etc. ........ But that aint easy, It can be done, but people who have always been worriers do find it hard - so it will take time and patience (just like breaking any other Habit), but in my experience we worriers don't have much time and patience for this kind of task and so just how bumpy you can expect the ride to be, will be in direct proportion to how accepting and patient you can be.
Hope it helped