Strange brown spots appeared on the leaves of the avocado tree. They appeared about 3 days ago when I accidentally overwatered the plant and a few hours later I opened the window to ventilate the room (I had taken the avocado out from under the window earlier). Today I watered (not overwatered) the avocado, then opened the window and moved it to a warmer place.Is it fungus or something else? And what am I supposed to do about it?