The tonal shifts in this film are something to behold, and I don't think they're intended to be so... Nauseating? It's hard to say, as obviously it's meant to progress (without spoilers) from one genre to another but it seems neither subtle enough to be a slow burn, nor deliberate enough to be intentionally (and the keyword here is "intentionally") jarring.
It's a real head scratcher... On top of the strange thematic shifts, the film suffers from characters that are unlikeable across the board, with the exception of Emma, and unresolved plot threads. To give it credit, I would say the first 40 minutes is interesting enough that you want to see where it goes, but personally I felt that where it went was unimpressive. It's not an outright "bad" film (as it manages to be engaging to an extent), just a poorly realised one.