What could this be & how do I support them?

Someone who is close to me has recently started having "internal freak outs" as they called it. Where they would suddenly disappear for a few days which usually results in blocking in any form of communication.

This happened for the first time last month and I was freaking out because I thought I did something wrong despite having a normal and wholesome conversation the day before. They did return after 3-4 days apologizing for "ghosting" because they had an internal freak out. I don't know if this is stemming from some sort of trauma/PTSD as they are in or work for the military.

This happened again for the 2nd time, we talked on the phone the night before then I noticed they suddenly disappeared a few hours later..

I don't know what to do or how to even be there for this person because also, I don't even know what this is. Help?

What could this be & how do I support them?
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