Arkro is an expert at masking negative emotions that make him seem vulnerable. An important skill to have, when you're both an assassin and a man on the run. So, when one notices the signs of him panicking, it's much worse than they think.
He will simply carry on as usual, hiding his discomfort as to not signal a moment of weakness. He becomes more deliberate in his words and actions as to not draw attention to himself. Maybe he'll even start cracking a couple of jokes as a distraction. If he's at a bar, he'll offer to make drinks for anyone in the vicinity, especially those he fears could be a threat.
But should a situation worsen, he will become slightly more snappy. He may play it off as a joke, but there's no denying he does become more hostile when he fears he's under threat. He would try to find away to leave the situation without being caught or questioned, even if anyone would simply ask him questions for benign reasons like concern. For all he could know, they have some ulterior motive and are planning to kill him. If he is in a position he has to take drastic methods, he won't even hesitate to kill threats if necessary. If he strikes or leaves first, he lives another day.
But if he is unable to do those things, well... If he has access to alcohol, he will start heavy drinking. He'll drink to drown out fear and become "funnier". He's got a lot of stories to tell, unrelated to why he's on the run, namely unhinged ex-boyfriends, so he entertains to distract others and himself. With how much he seems to overshare, he knows people will think of him as an open book and not question too much on what secrets he has. But he can become noticeably shaky, maybe even stutter and hesitate with his words when he is unable to do those two things or is pushed. He becomes increasingly paranoid of the people around him and may even request to become left alone. Perhaps his hostility becomes far more apparent and, even though he loathes being alone with his own thoughts, he may even isolate himself.
Only in the company of only himself, and maybe a bottle or two, does he truly begin to break down. Unless he trusts someone completely, he doesn't want to be seen in such a weakened state. He'll begin sobbing, perhaps even relive the horrific memories of what led him to his current path, especially on a rainy night. It's a genuine trigger of his, and he feels ashamed of it even though it was far outside of his control. Considering how he is, however, he will pretend to be perfectly fine once he's back in the presence of others. It's one of the only ways he feels his safety is guaranteed, after all.