Rhetorical questions

I've been hearing lately expresisons such as "I don't want that... Or do I?" or "I am so mad... Or am I?".
This seems to confuse me, since it looks like the first part of the sentence can be both in affirmative or negative form.
Are both correct?
thanks in advance.

Thanks for replying.
Maybe rather than rhetorical questions they are more like question tags, but my point is: are those two sentences constructed correctly? I mean, I've heard them, but that doesn't make them correct. I was dubious because question tags are usually constructed in the opposite form of the main phrase (i.e: if the main clause is negative the question tag is positive, and vice versa) and in both of my examples the 'tag' was positive.

Hello, Gillermicro.
There are four possibilities in English for question-tags: the verb in the main clause can be either affirmative and negative, and so can the verb in the 'tag', so you can have:

1- aff. main verb + aff. tag
2- aff. main verb + neg. tag
3- neg. main verb + aff. tag
4- neg. main verb + neg. tag

#2 and #3 are the ones that are usually taught to non-native speakers of English, but #1 and #4 are also widely used. Perhaps these last two are not taught at the same time as the other two because the meaning of #1 and #4 will vary according to the intonation used, and intonation is not something that -at least in my country- is taught in detail in schools of English in general, let alone in school.

Miriam

 "I don't want that... or do I?"

"I am so mad... or am I?".

 It sounds like quotations from someone who is confused and thinking to themselves,  trying to decide what to do.

In the first situation, imagine a lovely lady named Mary who is a little bit overweight. She is at a restaurant and having lunch with friends. They finish the main course and the waiter brings a delicious dessert tray with selections of ice cream, chocolate cake, and cherry pie.

Mary looks at the delicious desserts. She says to herself, "I don't want that ... or do I?"