It's a breathing issue, I would say. If you were being tickled, laughing your ass off, did a good bit of coughing, and the 'ler wasn't letting up, you likely weren't getting the air necessary, and in that case you can get sick. Just gotta try and make a conscious effort to breathe in more at certain times where the tickling isn't so bad, or your 'ler will have to learn about your signals and know when to give you a few seconds here and there to get some air.
It's the same with working out. If you're not breathing correctly, you can make yourself sick.
The stomach hurting from laughing I would say is normal, though, if you're not used to it.