Surprisingly hard for a simple game! Just a note, if you swap worlds when you get sent back to the past you die and it can be a little frustrating. Potentially add some of the other dimension at the start or don't allow the player to switch right away.
Also it seems to bug out when you die and you have to restart - oh and you probably shouldn't die from walking into the side of a spike, felt a bit harsh - cool concept though! GG!