Can obsessive thoughts etc go away then come back?

Can obsessions disappear suddenly? I've always went through periods of intrusive thoughts and periods without them. From ages 14-16 was sexual thoughts: about being homosexual (I'm not), raping children, any.. was pretty scary. From 16-18 mostly about hurting someone. 21-22 was numbers, but I also had obsessions with numbers when was 17-18. But wasn't all the time - sometimes was stronger, sometimes was off, sometimes was mild. I could go weeks or months without any of those intrusive thoughts, and then for 3 weeks not have one day without them. I also had a tendency to put things symmetrically and organized, but spontainsely. I can have a messy table in front of me, no problem. But if my mind says "you need to organize it" - it won't shut up. Even if now it's cleaner than was days ago, when didn't bother me.

I never really thought about what 'it' was because I thought was just me being a weirdo and if wasn't daily then wasn't bad enough to be a problem. Even if it means I couldn't watch certain cartoons when babysitting my cousins because triggered sexual mental images, or need to constantly put knifes against the wall and paralel to it. Or how I couldn't take a school exam without putting everything symmetrical and on its right place. Pen, then pencil, then eraser then calculator if was needed one - writting paper on the right, exam paper on the left; leave the identical border on all sides of the table etc. I had a teacher once, on purpose, drop my exam paper completely random and say "if you touch it, I will fail you". She made the whole class wait 2 extra minutes before starting the exam, so she could see me panic. I think she found it funny how after 10 seconds I was digging my nails into the skin of my arms.

I did tell a psychiatrist about the numbers, and she said sounded a lot like OCD or could have OCD tendencies - but I didn't even mention about sexual, symmetry, hurting people etc. At that time, I was in a 'bad' period, where being in a car or bus was torture, because I couldn't stop scanning car plates looking for the good numbers or else someone would die. But then it got a bit better, and I stopped seeing that psychiatrist (long story short: I couldn't see her anymore, and can't get one now) so I never got to discuss those things. So NO, I am not officially diagnosed nor am I saying I am. My psychiatrist said she wanted to talk more with me to see if it actually was OCD or not - but never got the chance, like I said.

On a side-note: Can one have obsessional thoughts while sleeping? In the past year, I've noticed that sometimes my nightmares reflect those sexual intrusive thoughts. I will know I am sleeping, but my mind won't let me wake up. I will be in the nightmare and then wake up, now that if I move I will fully wake up but not be able to. And that will keep happening over and over, from 20 minutes till 40 minutes. When I do wake up, I usually I'm so much in panic and feeling so disgusted, all my day is ruining - and I'm afraid to sleep again. I've had sleep paralysis in my childhood-teen years, so seems both connected with each other. These don't happen anymore, last one that happened was probably 2 months ago. But I had some nights after that, that I fell asleep while telling myself "please don't please don't".