The difference talking to mentor once a week makes.
I've kept track of sleep, rest, general wellbeing and dissertation work time for a week.
I can see I rested an average of 82min/day (deep rest) and slept 8h. However, on the days I worked I rested less and slept less than average (probably when I need it most!) So Tuesday evening, Wednesday evening and Thursday I felt not so great.
So the next step is to rest the average amount every day and see how I feel.