I'm sorry you are struggling with this. And I'm afraid I can't tell you what the cause is. I would presume it's anxiety. But I don't really know.

I experience something somewhat similar sometimes. There are nights when I can't get to sleep or I wake up in the middle of the night & can't get back to sleep. I have this condition (I don't know what it is) that I describe as being like restless leg syndrome except that I feel it throughout my whole body 24/7. (I also experience some claustrophobia occasionally especially when it's hot outside, the windows are shut & the air conditioner is running.) Sometimes at night, when I can't sleep, that RLS-type feeling becomes so unbearable I just have to get up. So I do. I get up & do something akin to walking meditation sometimes for an hour or more. Typically once I return to bed I'm able to go to sleep.

You mentioned your experience with low iron. I presume you've had yourself checked out medically. I don't know if you've tried any anti-anxiety med's. I haven't. I think about doing so from time-to-time. I'm not on any medications of any kind at all currently though. So it would be a big deal for me to decide to try something like that. Back when I was still seeing a pdoc, I had mentioned what I experience to him & he suggested I try taking Neurontin. He said it would take away that RLS-type feeling. However I never did try it. And I no longer see him.