You can be completely wiped out and still be exactly on schedule. Tired isn’t the same as lost.

Feeling depleted and being off track are different measurements that get read as one. Exhaustion reports on your energy, not on your progress, and hard stretches consume a great deal of both energy and time without anything having gone wrong. Sometimes the work is simply expensive. Tiredness is what doing it feels like.

Check the actual schedule rather than the feeling whenever you feel behind. If the dates say you are fine, treat the tiredness as a rest problem instead of a performance problem. Sleep is frequently the entire correction.