As mentioned above, each day you fly you must be personally fit.
As stated on your medical certificate;
MED.A.020 Decrease in medical fitness
(a) Licence holders shall not exercise the privileges of their licence and related ratings or certificates at any time when they:
(1) are aware of any decrease in their medical fitness that might render them unable to safely exercise those privileges;
(2) take or use prescribed or non-prescribed medication that is likely to interfere with the safe exercise of the privileges of the applicable licence; or
(3) receive any medical, surgical or other treatment that is likely to interfere with flight safety
If you are unfit, AMEs want to work with you to get you fit again, this may or may not involve the CAA AMS depending on the circumstances.
For a variety of reasons some pilots do not wish to be fit again, is this the situation to which the OP alludes?