Feeling well while on a medicine is frequently a sign that the treatment is doing its job, not a sign you can stop. This is very common with antibiotics, blood pressure medicines, mental health medicines and treatments for chronic conditions, where the underlying problem persists even when symptoms ease.
Stopping too soon can let an infection rebound, allow a chronic condition to slip out of control, or trigger withdrawal effects with certain medicines. The temptation to stop is understandable, but it can undo the progress you have made.
If you feel ready to come off a medicine, raise it with your healthcare professional. They can confirm whether the treatment course is complete, whether you need it long term, and how to stop safely if appropriate.