How would you interpret the phrase ‘I’m not gone off’?
Does it have the same meaning as ‘I’m not mad’?
Thanks. It’s from A Farewell to Arms by Ernest Hemingway (Chapter Six).

the context:

"But I do love you."
"Please let's not lie when we don't have to. I had a very fine little show and I'm all right now. You see I'm not mad and I'm not gone off. It's only a little sometimes."

Question

How would you interpret the phrase ‘I’m not gone off’?
Does it have the same meaning as ‘I’m not mad’?
Thanks. It’s from A Farewell to Arms by Ernest Hemingway (Chapter Six).

the context:

"But I do love you."
"Please let's not lie when we don't have to. I had a very fine little show and I'm all right now. You see I'm not mad and I'm not gone off. It's only a little sometimes."

Answer

If a person "goes off", they either lose their temper (ie. explode/go off, like a bomb) or depart.  Would "depart" also fit your context?

Naturally, the non-standard grammar tells us about the character.

Answer

I'm not 100% sure, but the speaker could mean "i'm not crazy" when they say "gone off". Sometimes in english, you may hear a phrase such as "gone off the deep end", which refers to doing something crazy or becoming crazy. Also, "mad" can mean something similar to "crazy" sometimes, instead of "angry", depending on context.