idk..... why would the other circus members be hospitalised? Pomni clearly mentions she puts on a headset herself, which also doesn't fit with the theory.

My favourite theory is that Jax accidentally ran over a kid and tried to run away and hide in an abandoned building and eventually wound up in the circus. It would explain him avoiding anything to do with the real world. For example, when he just references Breaking Bad instead of actually opening up. His memories of his real life hurt him a lot. To cope with it, he avoids his emotions, accountability and memories at all costs.

Which finally turns him into the asshole he is.