I've had this obsession with numbers since I was a little kid. I would be sitting somewhere, or going to sleep, and I'd count. Count forwards, count backwards, count again. I'd count to 10, or count to 100, or try to count to 1000. If I had something I had to do, and didn't feel motivated to do it, I'd make myself get up and move as soon as I was done counting. I'd use the numbers as a force to motivate myself. I was prone to depression since age 12, and first diagnosed at age 15 after a suicide attempt. As I'm sure you know, depression leads to a lack of desire to do things. So I'd procrastinate about something, and then count to make myself do what had to be done. The strange thing is, I still do that today. I've done it now for most of my life. It's a weird thing, but it's not a major problem of any kind, so I never actually talked about it with anyone. I don't think I've ever mentioned it here, even. But I count when I have to get up for work in the morning, before I get out of bed I'll go to twenty, then backwards to zero, then to twenty again, then backwards again, until, finally, I tell myself it's enough and I can get up and go.
The obsessive thoughts are certainly not the worst problem I've had. They're not life-threatening and they don't ruin my life or anything. However, they are an incredible nuisance. Sometimes they are completely innocuous; for example, as certain word like "sing" will have a special feel to it, and I will have to say, "sing", in my mind to myself, over and over because I'll have this obsessive urge to do so. That's not a harmful thing. I'm sure it's not a normal thing either. But I don't consider it worth worrying about. Similarly, I have this habit of moving my feet compulsively whenever I'm sitting somewhere, and the only reason I'm even aware I do it is that my sister finds it incredibly irritating to see, so she snaps at me to stop it frequently. But, like "sing", this is not a real problem.