I have the same problem and can't put any pattern to it for the life of me! It's very frustrating that your abilities one day to the next can be so unpredictably temperamental. Following some bad fatigue days I have terrible broken sleep - it doesn't make much sense.

It appears like there are underlying, subtle patterns for most people, it's just a matter of identifying them taking into account other variables (like season etc).

It's scary that some of you are still experience this confusing predicament so many months and/or years later At 9 months, the constant evaluation and balancing is already so exhausting for me