HUGE Clots in my Menstrual Flow - Should I be Worried?!

I've always had an average to heavy flow, and I've experienced very small clots before. Nothing a regular heavy flow pad can't handle. My cramps have also always been fairly painful regardless. I am very regular, every 28 to 30 days. It usually lasts for about 3 to 4 days.

I just started this month's period this morning. It was very light at first and got heavier throughout the day (which is normal). Tonight, I spontaneously passed three HUGE clots. The first two I was literally holding in the palm of my hand (which they covered) - the third was just a little bit bigger than a quarter.

I showered and put on two heavy flow pads. I haven't passed another clot, but I'm still bleeding heavily enough to run down my thighs despite the pads.

The clots were about the color of cooked, red kidney beans, but the blood flow is bright red.

I have a little bit of a headache and I feel nauseous.

I am not, nor have I ever been, sexually active. I don't smoke, drink, or take any drugs, prescription or otherwise.

I don't know if it's relevant or not, but I did have my blood pressure taken earlier in the day (a few hours before the clots happened). I have had a history of on and off high blood pressure, and I had it taken on a whim. It was high (184/95, I think), which the lady who took it said wasn't hospitalization high, but I would need to get back on to some medication some time soon.

So, should I be seriously worried, or stay calm unless it happens again?

Thanks!

Vanessa