This may be normal but you need to be aware that if you develop a headache, a fever, a stiff neck, or the drip does not abate over the next 48 hours, you should call your doctor.
I am so glad to finally find someone that has the same problem as I do. I always had post nasal drip but it wasn't severe until I had nasal surgery for sleep apnea. It was so severe that I was gulping every 3 seconds to get the drainage down. I was being tortured and my Dr. kept giving me antihistimines that made it worse. I was so miserable that I had decided that if a Dr. couldn't find a way to stop the drainage I was going to end my life. Thankfully I went to an allergist and was put on allergy shots and it slowed it down tremendously. I guess the drainage I always had before that wasn't really bothersome was some type of allergy problem and when they removed whatever they removed it opened the flood gate. I would run to an allergist!