I stayed in the last room of the hotel, but didn't sleep.

Staying in the last room of the hotel will not have any negative impact on health or safety, and you can sleep.

After the guest checks out, the hotel room will be cleaned and disinfected. Even if it doesn't stay overnight, the hotel staff will clean and disinfect the room. If you are worried about hygiene, you can ask the hotel to clean the room again or change rooms.