So a couple of weird glitches happened while I was playing. One was that sometimes when I moved from one room to the next, it would instead act like I was moving from the previous room to the one I was already in, and I would be placed back in the previous room.
Second: After I died, instead of respawning me at the checkpoint, it instead reloaded on the room with the staircase to the next floor, and my character was not on screen. I could not move or do anything else, and was forced to restart the game from the beginning (reloading my save file didn't fix it).
Fortunately I was only on the third floor, so it wasn't that bad. Great game, by the way.
Also, why are there no invincibility frames?