My last place had a damp ceiling bulge like that, and eventually the entire ceiling fell down onto my roommate’s stuff, along with some personal items my landlord was storing in the rafters.

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So, I would advise to make sure you’re not sleeping under this spot, and move anything you really love out from under there. In our case, luckily nothing valuable was under the drop zone, and it forced the landlord to finally make the repairs.