A few honest thoughts, and I'll flag the tension up front: the clear-headedness you're describing is real and worth taking seriously — but stopping without telling your doctor carries some risks that depend a lot on which medication it is.
The part I'd genuinely validate: cognitive fog is a legitimate reason to change course. It's not a minor complaint to trade away for a slightly better lab number, and people often underreport it because they assume it's the price of treatment. If a medication is dulling your thinking, that's information your doctor needs.
The parts that worry me:
**Feeling fine may be the medication doing its job.** This is the big one. With blood pressure meds, thyroid replacement, antidepressants, mood stabilizers, seizure meds — "I feel fine" is often the treated state, not a cured one. The relapse can take weeks or months to show up, and by then the connection isn't obvious.
**Some medications shouldn't be stopped abruptly.** Beta blockers, certain antidepressants, benzodiazepines, steroids, anti-seizure meds — stopping cold can cause rebound effects that are worse than the original problem. A taper would have been safer.
**Early clear-headedness can be ambiguous.** Sometimes it's genuine relief from a sedating side effect. Sometimes it's a discontinuation effect. With mood-stabilizing medications specifically, a sudden feeling of sharpness and clarity is occasionally an early sign of a mood shift rather than a return to baseline — worth knowing, not worth panicking over.
What I'd actually suggest: tell your doctor you stopped, and say why. Not to get permission to have quit, but because they can't help you find something better while thinking you're still on it. Frame it as "the cognitive side effects weren't acceptable to me — what are my options?" Dose reductions, switching within a drug class, changing timing, or a monitored trial off the medication are all normal things to negotiate. A doctor who won't have that conversation is one worth replacing.
Can I ask what the medication was, and how long ago you stopped? The answer changes substantially — an antibiotic you quit halfway through, a statin, and a mood stabilizer are three very different situations.