There are some people who are very, very idealistic, to the extent that even when they are sick, they think such thoughts as "I've got sloth and torpor, I'm no good, I'm just terrible, and so on". Now I actually know someone who was sick one afternoon, but they didn't know they were sick. I didn't know they were sick, either. They were just talking about how they are full of sloth and torpor, that they are a lousy meditator, that they are this and that. Early in the evening, they fainted, and fell down in the bathroom, they were rushed to the hospital. They had food poisoning, they didn't even know it. So it's very important to be able to tell the difference between, in this particular case sloth and torpor and actual exhaustion or illness, and to guard against having a similar sort of situation arise.
Now you can ask yourself as to your mental state, when you are exhausted it's a physical thing and the mind is kind of out of it, also. When you have sloth and torpor however, it is usually not a physical thing. The mind is out of it, doesn't want to do anything, and the body kind of is like that, too, but there is a difference there and you have to be able to pick up on this. There is no quick and easy way to do it, it often takes time and experience but this difference between being exhausted and having sloth and torpor is very important.
One thing that you can do in everyday life to maybe prove whether you have exhaustion or whether you just have sloth and torpor is to put yourself in a situation that is interesting, really, really interesting. And the same applies with meditation subjects, use meditation subjects that are very interesting. If you are exhausted, if you are absolutely exhausted, if you are ill, whatever, it is still not going to get you anywhere, you will still be exhausted and ill. But if you have sloth and torpor and you make things interesting, all of a sudden the sloth and torpor is going to go away. So you have to experiment.
Whenever you feel that maybe you have sloth and torpor or maybe you are exhausted, see if you can actually stimulate the mind by changing the meditation subject. Now of course sloth and torpor doesn't want to change the subject, sloth and torpor doesn't want to do anything, so it is a difficult thing to work with, it will take a little bit of practice and then hopefully you will be able to see for yourself. To let go of idealism helps so that you can see more clearly if you are really wiped out or not. You have to decide for yourself if you actually physically wiped out, or if you are just mentally avoiding something?