There’s a big difference between believing in the work you do and being in a good mood all the time.
“Follow your passion” doesn’t mean (or at least it shouldn’t mean) “always feel amazing, enthusiastic, happy, and inspired.”
You can have bad moments, neutral moments, sad moments, sober moments, serious moments, inspired moments and all other sorts of moments and still live a deeply passionate life.
In your quest for meaningful and fulfilling work, don’t make a god out of your emotions. Go after the things you love, but don’t confuse love with always being cozy, comfortable, or cheerful.
You’re more than your feelings. As such, you have the capacity to create value or discover meaning in any emotional state. So even if you feel like you’re not on top of the world, don’t give up on the world and don’t give up on yourself.
Instead of measuring your worth or success by how you feel at random moments, measure your moments by how successful you are at finding things that are worth believing and doing no matter how you feel.