When I feel down with some bad news and don’t want to talk with anyone, but I have to. I hide my real emotions and act cheerful.
In this case, how can I describe myself, “I fooled myself.” or “I faked myself.”
I’m very nervous at the speech in front of the people, but in order to hide my nervousness, I pretend to be confident. In this situation, can I use the either sentence?
Or if there are any other sentences for these situations, could you explain them?
Neither of these phrases are appropriate for what you are trying to express.
To fool someone means to deceive them, so saying that you "fool yourself" would mean that you are tricking yourself into believing something that is false.
The phrase "fake myself" sounds odd. It would be better to describe the state that is being falsified, e.g. "fake confidence."
In my opinion, other words are better used to describe this situation, many of which you used in the body of your question. The verb "act" implies that one is faking. To say that you are "hiding" your true emotions is also a valid way to express this. Here are some more suggestions:
I acted strong despite my weakness.
I chose to hide my anxiety.
I smiled with manufactured confidence.
I responded with optimism I did not feel.
I tried to cover up my mood with pretend cheerfulness.
(Note that "pretend" is used as an adjective in my last example.)
Another word you might consider is "feign", as in "to feign confidence".