In Milindapanha it is said (Book IV, Chapter 1, §63)
Nagasena says:
‘If, O king, all diseases were really derived from Karma then there would be no characteristic marks by which they could be distinguished one
from the other. When the wind is disturbed, it is so in one or other of ten ways–by cold, or by heat, or by hunger, or by thirst, or by over eating,
or by standing too long, or by over exertion, or by walking too fast, or by medical treatment, or as the result of Karma. Of these ten, nine do not
act in a past life or in a future life, but in one’s present existence. Therefore it is not right to say that all pain is due to Karma. When the bile, O king, is deranged it is so in one or other of three ways–by cold, or by heat, or by improper food. When the phlegm is disturbed it is so by cold, or by heat, or by food and drink. When either of these three humours are disturbed or mixed, it brings about its own special, distinctive pain. Then
there are the special pains arising from variations in temperature, avoidance of dissimilarities, and external agency. And there is the act that has
Karma as its fruit, and the pain so brought about arising from the act done. So what arises as the fruit of Karma is much less than that which arises from other causes. And the ignorant go too far when they say that every
pain is produced as the fruit of Karma. No one without a Buddha’s insight can fix the extent of the action of Karma.’
kind regards,
Siebe