I hope they gave you a medication to help you deal with the post traumatic stress disorder, which stress is the key word there. Stress can goof up a person's sleep, which that is how come a song or phrase will trigger your coping mechanism. You cope by daydreaming and writing and that sort of thing.
I am a writer, and the way I learned to finish my stories, which is also known as "not knowing how to write the third act," is I wrote short stories for a while. And I mean short. I started out writing an entire story on one page. Not easy to do! Only takes a couple weeks to get that down pat. Alternate stories with poems. They are also very short by nature. Another way to "finish" the creative process is to add one more creative skill to your habits, which art works really well for me. I use very small canvases, just abstract stuff, and when I fill the canvas, I am done.
I would suggest you take a writing class, just part-time at the local community college. They will teach you about the individual parts that make up a story, like character studies, themes, beginning, middle and end of stories, that sort of thing. This is because I think you could channel this wonderful talent you have into something that might make you some money! Imagine being able to spend the whole day on your daydreams! However, it is hard to make a living as a creative personage, so sometimes people have to do more practical variations on their talent, in between their fun stuff, like many writers become reporters on newspapers, script writers or other workers on a film set, that kind of thing.
As for focusing on the job at hand, which is probably the hardest thing in the world to deal with, because EVERYONE is not too thrilled about paying attention all day, when they'd rather be doing something else, is you have got to practice holding back that stream of consciousness going on in your head. You do it through a reward system. For example, I have to paint and clean up a room in my house. I'm like you, I tend to put the paintbrush down and wander off and forget what I'm doing. So, I've got it arranged so that when I finish doing everything in that room, I can then "decorate" it, which I love that because it's creative. So, when I'm done, I'm going to go out and waste some money on some pillows for that room, because I like to shop and buy pretty things, but I feel guilty spending the cash, so that's my reward. It will "complete" the room in a very pleasant way. If I keep my mind's eye on that reward, it helps me focus.
People who work the whole week, they keep their mind's eye on Friday. They cannot wait for that day. And everyone comes to work that day feeling mighty good, the pace picks up at work, folks talk more, they wear their best clothes, because they know that they will be able to walk away from a week's work well-done, collect their paycheck, and THEN go do what they WANT to do. It's a matter of maturity, responsibility, duty. ANYONE can stand around on a street corner and hum all day. But it doesn't pay the bills. And street people don't contribute to society, which is an important spiritual value.
You have been to hell and back. It's time to come back and be everything you can be in this wonderful world we live in. The past must stay in the past. The future is yours. I hope some of these tips will help you find your way out of the dark and into the light, so you can learn by practice to manage your emotional mind-set. The rewards are infinite. And it doesn't matter anymore how you got the way you are. What matters is what you do about it now. It is how you behave, which is call behavioral psychology. You "do" your way out of your situation. I am glad you posted here, that was very brave, and it shows you are READY to move on now.