It is all too easy too rationalise some of the symptoms of burnout as @eliboy stated in this thread as being 'other things' and ignoring the bigger picture. For example, if you are feeling tired and sad, is it depression or early onset burnout, or are you just suffering lack of sleep? Or just dehydration? Or is it because you had a late night out a couple of days ago?
Left to your own devices (especially when you are already burning out), it is all too easy to diagnose it as the latter causes, especially as your reasoning ability will be diminished.
Many times I have felt overwhelmed to the point of paralysis, thinking that it was because I couldn't say "No" to new projects, but it ended up being pure burnout.
Oh, and the frequent 'cure' for burnout from many of my colleagues is to force me to take a break and do nothing for a while. That actually makes it worse for me. I find that my best solution for burnout is to actually WORK HARD at another passion of mine - for example, If programming gets me down, I will go off and learn a fiendishly difficult piece on classical guitar instead. Others are horrified that I am putting my brain through more gruelling stress, but I find that thinking about music rather than programming for a while tends to help me feel creative and refreshed again.