Do you agree?
I don't really agree, personally. Too me, it is one of the best seasons. Right between summer and winter, the weather is almost always "just right."
For your thesis, don't state "most feel low..." because many of the readers may find otherwise. Simply just say "while some like fall ... others think that fall makes them feel low... etc"
Do you see what I mean?
For the body paragraphs, think of reasons
why fall would make someone feel low and enervated. You could even use scientific facts if you can find them. Experience with others can also help.