I try to do two things:
-
Keep a schedule of doing reviews twice a day (morning and night, usually while eating breakfast and just after dinner). I might not be able to do all the reviews – I use either the wrap-up button or @Kumirei’s "Review Queue Sizer” script (see this thread) if it’s really too many (like 200 and I only have time for 50).
-
Only do new lessons if the forecast for the next day for the number of reviews do looks reasonable. I don’t worry too much about getting behind on lessons. Language learning isn’t a race, after all, and it’s better to keep to what you can manage.
Even so, I have burnt out a few times and had to take breaks for a few days. When I come back, I just try to get back on schedule and tackle reviews in manageable chunks.