A guest staying at a Gramercy Park hotel killed himself early Sunday afternoon, cops said.

The unnamed man “put a bag over [his] head” in his sixth-floor room at “The Marcel At Gramercy,” police told The Post.

Authorities said the bag had a “feeding tube” stuck in it and “some kind of toxin was sprayed in” through the tube.

The man’s body was found by hotel staff about to clean the room.