When you relax and zone out, what brings you back?

So, I may have personally issues. I've had a stressful childhood, and I dont think I've ever truly relaxed.

Recently, I think I found out why, and I have pretty powerful want to stop worrying about things and relax for once, for a bit, to recharge, but it feels a bit like dreaming. (Maybe I'm just really tired)

When I sleep, eventually because I'm no longer tired, I wake back up. With relaxing and zoning out, it feels intentional, and not based in a need to "fill a sleep meter", so I dont know what makes you stop I guess.

I worry a bit that if I relax like this, I'll sort of get lost. It's a bit scary, I've always been high-strung and on alert, to the point where that just became me and felt natural. Now I'm not sure what's me and what's just being on alert and dealing with problems.

If I was in a totally shut off room, it feels like a valid threat to me that I could relax and let my mind wander and be stuck like that forever.