Going off Plaquenil can often trigger a flare, putting you back in a bad place. Feeling good while on Plaquenil is generally a sign that the Plaquenil is doing its job-- keeping your autoimmunity at bay. Stopping it can let everything rev back up.
Plaquenil is a long-term, disease-modifying drug.
Regardless, don't make a decision to stop Plaquenil without taking to your rheumatologist. He or she will be able to discuss with you whether it is safe to stop the drug. Some people go into true remission and stop Plaquenil, but you really need to talk to your doctor to see if that is the case with you.
Good news that you're feeling well! Congrats on that.