IN general, overflowing a Keeper in 10 hours at the beginning of a period isn't excessive, except that this isn't normal for your cycles. Since the bleeding is slowing down, I probably wouldn't worry too much. I've had unusually heavy periods and just chalked them up to temporary hormone imbalance or something. Last year, I had a weird period which was heavy and then, just as it was slowing down, I yelled at my kids and suddenly started bleeding heavier and passing clots. I was freaked out and went to bed all worried. All turned out well and my periods are fine now. The weird thing is, when I had this heavy period, I was also coming down with the worst illness I've ever had (mystery virus--still don't know what I had). It took 4 months to recover and during that time I had terrible--lie-on-the-bed-crying--cramps that are totally abnormal for me. My midwife said that illness can absolutely do weird things to your cycle.
Not to scare you--I'm sure you're not about to get really sick. I'm just saying that changes in your body such as illness or stress or travel can mess up your periods. I also remember a few years ago that we did a lot of travelling and during that time my periods were unusually heavy and crampy.
I hope everything goes back to normal by itself.