Actually I find it to be the opposite. When in poor health the mind and body become preoccupied with trying to heal itself so a lot of energy gets spent on the process. Also conditions like high fevers, aches, body pains, nausea,etc all make it difficult to reach a state of calm anx relaxation that would allow a person to let go from themselves. (for lack of a better way of putting things.)
In a more general sense- placing sicknesses aside, there can be some interesting correlations between people who are less physically inclined and more scholarly. But that is more physical condition reflecting personality type. Philosophical study, introspection, investigating ideas and their histories and readonings, these are all exercises of patience. It is a long and constant term of learning and study that tends to come more naturally to people already predisposed to learning over physical activity and adventures.
I find it all depends on what you are trying to do and how strong your mind is. If you are psychologically or mental weak, or tired it is not the best idea or easier to do. For the very fact A.P. is mostly done mentally. But body wise it may be easier because depending on why your body is weak your mind might find it easier to escape but I do agree with the other comment there is a chance you will have a hard time if what is making your body weak can preoccupy your mind.