I find the same thing happening for me too. I have been doing this (on and off) for just over a year now. For me, it is not just funny things, but all pleasant sense-experiences, such as food, sights ect. seem to lose some of their "magic" when I try to be mindful of them. They suddenly don't seem that great any more. I do also sometimes miss being immersed in them, especially as I am currently trying to remain heedful and aware throughout the whole day.
I think in the long run, this is a good thing, as it is the beginning of seeing the Dukka inherent in conditioned things, and the drawbacks of sensual pleasure. Not necessarily a good thing if one wants to remain a housholder
. Perhaps the best advice, though I am not experienced enough to be sure myself, is to just carry on and push through it, and immerse yourself in the joy that the path gives.
"If beings knew, as I know, the results of giving & sharing, they would not eat without having given, nor would the stain of miserliness overcome their minds. Even if it were their last bite, their last mouthful, they would not eat without having shared."