It is believed that promises made when one is happy is not taking to heart. Such promises are made under the euphoria experienced by the promise maker. Promise made when one is happy is like a steam of vapor expelled into the atmosphere which literally would not be accounted for as part of the boiling water.
However, people have the propensity of making flimsy promises that they cannot fulfill; generally speaking now, even when made under unexcited mood. What can one expect then of a promise made when one is super exited about something? You will know that it's like a weightless words uttered by a drunkard, and if he's asked the next day about what he said, he won't be able to recollect his words.
Advisably, never rely on the promises made by someone that is not in serious mood, because if you do, it might just be your undoing by the time your expectation of such promise is met with disappointment.