Two examples of iatrogenic conditions, one trivial and one serious :-
False hypertension. It's extremely common that your blood pressure, when taken by a doctor in his clinic, may be quite a bit higher than its normal resting value (for instance, if you immediately go home and take it yourself with one of those blood-pressure meters which are now commonly available for self-use, you may well find it to be ten or even twenty points lower).
This is presumably a psychological or nervous effect, even though it occurs when the subject may in fact feel perfectly at ease with the examining physician.
Cross-infection with methicillin-resistant Staphylococcus aureus (MRSA). This is far more serious and is becoming, in hospitals in the UK at any rate, more common than it was a decade ago.
Staphylococcus aureus, the 'golden staph', is often found, harmlessly, on the skin; but if it is transferred to the bloodstream or elsewhere, either during an operation or via a recovering surgical wound, it can produce an extremely dangerous infection --- for instance, septicaemia --- and is responsible for a number of hospital deaths each year.