I can well believe that, I bet the adrenaline rush of a first contact is insane, it wouldn't be surprising if it was very addictive in a strange way. I also wonder if some/many cases of PTSD is caused by the comedown of returning to 'boring' civilian life rather than just traumatic experiences....is it possible that exposure to massive adrenaline surges does something to people when taken out of that environment?
I've worked with loads of ex military guys often paras, marines and especially French foreign legion, as someone who has never been in the military but very interested in history