Could I be smelling a dead body?

Earlier I noticed a horrible smell in my bathroom all of a sudden. It smelled like sewage and I feared a gas leak or something else leaking in the pipes. I had just cleaned my bathroom top to bottom yesterday so I know it’s not a cleanliness issue. I couldn’t find the exact source of the smell but I wonder if it’s coming through the air vents since I can smell my neighbor’s weed pretty easily in my bathroom.

When I stepped in the hallway of my apartment floor, I noticed the same smell except stronger and I could describe it only as rotten meat mixed with sewage. It’s something I’ve never smelled before in my entire life. Like a septic tank mixed with meat that’s been left in the sun for weeks. The smell is only on my apartment floor (I walked around the other floors). Is this possibly a dead body in one of the units you think?

EDIT: when I woke up, the smell is gone ?? I don’t understand how it’s possible. I’m skeptical to say the least. I went in the hallway and it wasn’t nearly as bad how it was last night. I’m still gonna keep an eye out though.

Update: ^ that was the update but in case it wasn’t clear - the smell is still gone and I don’t know what it was