Me again,

I posted a week or so ago about how I was doing much better but I seem to be going through an anxiety relapse. I was on Prozac for a few years (60mg) however, about a year ago, I went off it cold turkey. Since I'm going through this "blip" my Dr. put me back on Prozac - starting me off at 20mg. Im on day 3 now and I am hysterical. I've convinced myself I have serotonin syndrome. This is not a new fear, every time I start medication I'm afraid of serotonin syndrome. I also take Mirtazapine (15mg) I've been on it for 15 years (helps with sleep.) I'm convinced the combination is going to cause me to have serotonin syndrome and even though I've taken Prozac before (with mirtazapine) and I never suffered from serotonin syndrome, I'm convinced this time will be different. All day I've been in a fog, everything feels strange, I began crying hysterically, my hearts racing, my pupils are not dilated, I feel dizzy, hot, feel like I'm going crazy, like I'm losing my mind, chest is tight - all panic attack symptoms I know but I just can't get the serotonin syndrome out of my head and I can't stop feeling like I'm going to die.