from me "stupid" training for 27 years...and never was real ill in that time....my longest "off" from Training was 12 Days...that was on holiday....When i`m feeling real sick, i don`t go to the gym, but that happens maybe 3-4 times in 27 Years of training.
Sure, sometimes there is a thin line between "to go" or "not to go", but the Body tell you what`s right or wrong.
It`s also sure that Bodybuilders tend to overdoing things....but, i like to work out, and i see so many people which are only training from time to time, and telling "i was sick, i had this, i had that....and so on", and wondering why they never build a real muscular-physique.