Tips for Overstimulation

Hi, I was debating ppsting in here bc I am not diagnosed, yet. But not going into detail, I know this is the only place I think I could advice about this.

I am 23 years old, I struggle really hard with overstimulation. Everyday I am overstimulated, I wake up that way, and even the smallest thing can push me right over edge and into insane meltdowns. That is why I am here.

I hit myself in the head, a lot. It's the only thing I've ever found that helps. I've read so many posts from different people about it. I fear the reason it helps is because I am trying to hurt myself. I get extremely bad thoughts about it in the moment. It's getting to the point where my head is pounding due to it. I am really scared I'm going to do damage. I don't know what to do.

I've read other people's advice on other's posts about it, but punching pillows, ice, eating something spicy or cold, none of that works. And I can't hit other parts of myself, because I will not stop until I am genuinely hurt.

Any advice at all would be appreciated. I'm really embarrassed by it, I feel so helpless. Thank you to anyone who replies.