The season's ill – (line 13)
This doesn't exactly scream, "my mind's not right!" but it's the first major sign of our speaker projecting his mental illness on the state of the town.
One dark night, my Tudor Ford climbed the hill's skull, (lines 25-26)
The speaker is going into the dark, dreary place in his memory.
My mind's not right. (line 30)
Here's the hard evidence. He admits to feeling off.