An unidentified man was found under a mattress inside a midtown hotel room Monday with trauma to the back of his head, police said.

The man, who police have yet to identify, was found at about 4:10 a.m. in a room of the Hilton Garden Inn on 35th Street, near Sixth Avenue. He was found under the bed.

Police are reviewing videotape from the hotel and are looking at three men and at least one woman who were also in the room.

A manager at the hotel was not available for comment and a representative for the hotel did not immediately respond to a request for comment.

By the afternoon, it appeared to be business as usual outside the bustling Herald Square hotel. Guests came and went, seemingly unfazed by the grim discovery hours before.