Gabapentin seems to be pretty effective for me now. I had some side effects when we moved to 1800 mg per day, backed off to 1200, and now things seem pretty stabilized now. I'm not noticing any side effects, which is a very welcome change from Lexapro.
You have received some very good information already. Although anxiety attacks can go on like that for hours, and sometimes be anxiety without the fear component, I would be more inclined to look into the cardiophysiologic explanations, and treat the symptoms accordingly. If gabapentin works, it is a good medication for you..but pursuing the "why" is still a good course of action.
I've wondered about things like dysautonomia also. My regular doctor and my therapist have both questioned whether my anxiety is following some physiological symptom that I've just gotten very worried about.
Rob2008, your symptoms sound like they might possibly be symptoms of dysautonomia like POTS, rather than anxiety. The lightheadedness is typical, along with the high pulse, and hydration and lying down would be typical methods of alleviating the symptoms. Changes in blood pressure are also very common. Particularly if you're not feeling anxious, this is definitely something to look into. The test to ask for is a tilt table test; usually you need to find a good cardiologist to be knowledgeable on this.
I get these exact same symptoms, it lasts from maybe 30 minutes - 2 hours at a time and my pulse is around 110 or so resting...often i feel lightheaded. The only thing that seems to quicken this to stop is a glass of water and laying down for 20 minutes. Blood pressure is very erratic during these episodes. I don't really feel anxious either, just symptomatic.