Rest should happen before your body begins demanding it through failure.

The body has a sequence of requests, and it starts politely. Poor sleep, small illnesses, a persistent ache, irritability. If none of those are answered, it eventually stops asking and simply stops you, at a time and in a manner you do not choose.

Rest on a schedule rather than on demand. Decide in advance when you are not working, and keep it even in a week when it feels unnecessary. Especially in a week when it feels unnecessary.