Is it like a normal day and you say to yourself "Oh well, it's not a big deal, it's only one day."
Or perhaps you feel guilty?
Usually people feel some degree of guilt, similar to forgetting to feed a dog or another pet.
It actually hurts.
It hurts because you feel responsible.
Responsible not only to yourself but also to others, especially your family who tolerate your hobby or organ practice but they want to see the results, they want to feel you are being serious. They want to know they are betting the right bet.
And when you skip organ practice, you know they feel disappointed. Disappointed with you and with themselves that they trusted your commitment is serious and long-term.
Your responsibility can also be for other people who are counting on you - your congregation, your closest fans who will come to your recital.
And you know that your time is limited. Your days are limited.
So when you skip organ practice for one day, this day is gone forever. Opportunity to reach your full potential is smaller.
Only if it's for 15 minutes, even if it's on the table without the instrument, it still counts.