OK, again...
Most religious people I've met are pretty happy, and religious belief, no matter what any of it's adherents will tell you, is a hugely restricting thing.
I've been talking about both.
Following an organised religion is most restricting of one's life. It tells you how to act and behave and think in many ways. It is anti-freedom. Whether it's anti-happiness i don't know.
Instead of celebrating some mythical God, celebrate life instead. Do some meditation today and celebrate life today. Celebrating life is not restrictive. Meditating is surely about dropping all restrictions.
If celebrating life is religious, then i'm religious. But that's not the same as man imposing themselves on another's life through antiquated beliefs and myths from a long bygone era, since when we've evolved by quite some way on several fronts.