While on paxil can you get used to the dose and get side effects while on it?

I have been taking 20 mgs. for 3 months and for the last 2 days have had these strange headaches behind my eyes and nausea. I am wondering if you can get used to the dose of paxil your on and start having some withdrawal effects even though your still on it. I refuse to increase my dose after reading all the horror stories of withdrawal. I know sometimes with other meds your body becomes used to a certain dose and you need to increase it to have it work. Has this happened to anyone else on Paxil? It really works well for my panic attacks. Any help??