Singing when you feel nothing is still worship. Maybe the purest kind.

Doing something you do not feel is usually called hypocrisy, and here it is closer to the opposite. When the feeling is absent and you show up anyway, the action is stripped of everything you might be getting out of it. What remains is a decision. That is why the flat version can be the more honest one.

Keep going to the thing on the weeks it does nothing for you. Sing it, sit in it, say the words without waiting for them to move you. Do not judge the practice by the temperature of the day, and let the steady unremarkable version count as fully as the good one.