Not exactly, but close. "Feeling" is an adjective. You cannot replace it with "experience" in your sentence because "experience" is not an adjective. Thus the sentence I'm experience optimistic (WRONG) doesn't make sense. You would have to say I'm experiencing optimism (CORRECT) and that makes sense and means almost exactly the same thing as your sentence. This raises an interesting question. Why is one of these sentences good and the other bad: I'm feeling optimistic. (GOOD) I'm experiencing optimistic. (BAD) The words "feeling" and "experiencing" are almost exactly the same, and yet one sentence is good while the other is bad. The reason for this is that the verb "to feel" can be used as a "linking verb" to connect subjects with adjectives whereas the verb "to experience" is not allowed to be used as a linking verb. If you read about "linking verbs" and "adjective complements", you will understand this better.

It means how you feel. Your feeling or mood.

Feeling equals a state of being.