Rest days are part of the plan
Athletes plan rest. Habits deserve the same.
A habit that only works when everything goes right won't last a year. Illness, travel, a busy week at work and holidays are part of every year, and a plan that counts them as failures teaches you to give up.
Rest is not a miss
In Mostly Daily, rest, low energy and travel days are real states. They don't help your level and they don't hurt it: the day simply doesn't count as a chance to do the habit. Low energy days never use the rest budget; rest and travel have a soft monthly budget, so rest stays a choice rather than a way out.
Plan time off
Going on holiday? Set time off for all your habits at once, or only for the ones you choose, and give it a reason: Vacation, Low energy or Other. Reminders go quiet, nothing counts as missed, and when you come back you get a calm welcome, not a list of what you didn't do.