I have been on Paxil for about 15 years. While I have not have any cognitive decline, as paxiled said it is a difficult medicine to get off of. I still have anxiety here and there and that can be expected as medicine will not solve the problem but rather band aid it. Therapy is a much better alternative to medication, particularly CBT. However, if medicine is necessary I would not go to Paxil. I belive there are much better alternatives out there and if Paxil wasn't such a beast to get off of, I would likely choose another SSRI.
By the way, I still take medication -- I am one of the ones who didn't find an alternative that worked.
By the way, there are no "safe" drugs. They are all artificial to the body, and antidepressants are more artificial than most in that they alter the way the body normally uses neurotransmitters. Drugs should always only be taken when all else has failed. Because the body is incredibly adaptable, most will do fine, but if you're one of the ones who doesn't, it isn't any fun. But if you need them, then do your homework and learn how to use them as safely as possible. It's the best you can do.
Any drug that affects brain neurotransmitters can have unusual consequences, but this is probably a very rare side effect if it exists. Antidepressants do, however, and this is unknown to most users and doctors, usually affect choline receptors, and choline is very important to normal brain function including cognitive ability. Paxil is the strongest of all of them, I think, in its affinity for choline receptors. The biggest problem with Paxil is it's almost impossible to comfortably stop using it after long-term use, and many believe its strong affinity to choline receptors is one reason for this. It's just a very strong drug, for some reason, and is very very hard for most people to stop taking. I can't say I ever suffered any cognitive decline from taking it for many years, but I've suffered everything under the sun after stopping, but my reaction was rare -- still, this is the drug that started the whole withdrawal recognition, and I'd only take it as a last-choice option. The same, by the way, is true of Effexor, an snri, for the same reasons.