I realize that this post is kinda old, so I'm pretty much necroposting, but I just wanted to add a few things.
Hope I'm not making a bad first impression. = S
I'll start out by saying that everybody stims Some people do it in more discrete ways, like playing with their hair or biting on the end of a pen or pencil, while others do it in more obvious ways, like rocking, hand flapping, etc.
I have schizophrenia, and I stim a lot. I have a couple different stims, but my most common ones are rocking and rubbing my thumbs on my finger tips. I also have sensory processing issues and my therapist says that some of the things I do in relation to that could also count as stimming, such as how I almost always have something in my mouth.
Now for your questions:
1. Many of the stims I do are the same as the stims that people with ASD do.
2. I use stimming for lots of different reasons. I use it to calm myself, self regulate, and when I'm anxious, scared, or just bored. Although, I have noticed that I do stim sometimes when I'm really happy. So I guess I stim for pretty much the same reasons.
3. From what I've read about what it feels like when a person with ASD stims, it's pretty much the same.
One last thing, please don't say "schizophrenic." Some people don't mind, but others of us don't like it. When saying someone is a schizophrenic, you are defining them by their illness. I am not schizophrenic (literal definition: character of schizophrenia), but I do have schizophrenia. Therefore, I am a person with schizophrenia, not a schizophrenic.
Hope I helped!