the second I start to act out of character, the urge just vanishes and I feel really stupid.

I have found this too.

In shamanism, this happens a lot, the first time a person starts drumming, or dancing, or rattling. It can feel very stupid to rattle a rattle as an adult! The advice I have been given is to just keep doing it until the stupid goes away. Until your inner adult throws all it can at you, and then says 'oh stuff this, I'm going elsewhere, do what you want to do.'

Have you ever tried persisting through the feeling of 'stupid' that you get?