I'd agree that "tired" ie, without energy or running on fumes isn't sustainable. But I'm more speaking about the ups & downs of "tired." If you don't have the energy to do what you're doing and are using something else to get you through each day, ie, way too much caffeine, drugs, etc. Then yeah, you gotta make some changes.
totally agree. I've been tired for 3 years and eventually you discover you just have to give sone things up or not operate at full intensity at all times. otherwise you'll be doing everything crappily