I think it's pretty canon that Hiccup, being a premature baby, experienced exercise intolerance at least to some extent so like
I think that training with Astrid and maybe flying with Toothless would actually make it somewhat better over time but also post first movie, maybe even during rtte, something happens and he rapidly overworks himself and just steps aside to puke in peace just to come back like "yeah, that happens sometimes :)" while the gang is just like ??? are you ok???











