I could see him having abandonment issues, and part of it being justified to him by how dangerous it is for him to be alone on the battlefield (although mitigated if he's going battle medic and hunting someone down). He's afraid and missing the comfort his caregiver provides, especially in his regressed state. And given he's back to a time where he wasn't able to regulate his emotions, the overload makes him just wail and bawl his eyes out until they come back. They find him with his hands over his teary face, eyes puffy and still crying and hugging himself in an effort to self-soothe. Then upon noticing they returned, pulls them down and close to him, demanding they snuggle.