E brake + ABS + constant alarm went away

I'm driving a 2006 Prius with 82k miles. I bought the car in December, 2017 with 48k (!). I have been doing solely oil changes at 5k intervals and tire rotations at roughly 10k intervals. I haven't had any mechanical issues.

Recently, as I was banking out of a turn, the emergency brake and ABS lights came on, along with a constant alarm. I was only a few miles from home, so I proceeded there where I was able to park easily despite losing power brakes. I turned the car off, and when I put my foot on the brake to turn it back on the alarm started again. When the car came on the large triangle with exclamation point lit on the dash. I decided to check the fluid levels and leave it alone for a while. I only noticed that the inverter coolant was about half an inch below the low mark, though I don't know how long it has been low.

A couple hours later I drove with no issues. In fact I met up with a friend who owns a Prius and she said she has the same issue when she is due for an oil change, which I was at the time. She said that while going around a turn, the fluids would slosh and cause some sensor to alarm. Is this a legit explanation?

I wanted to get my oil changed at the dealership for the full 5k service, but it didn't work with my schedule and I went to Jiffy Lube. They said there was an engine oil leak, but since this could be solved with their special high mileage oil, I thought it might be BS. They didn't know anything about the coolant, so I bought some super long life to top it off.

I called the dealership to ask about the issue and coolant and they said since it involved the brake system I should definitely bring the car in. Does this seem necessary? My theory is, since I was driving on a gravel road with puddles and potholes right before the banked turn, I might have hit one too hard and triggered a sensor somewhere? Or created a leak. I will continue to monitor the fluid levels and check the 12V battery just in case.

I probably should have just waited to get the 5k service at Toyota, but I wanted to get all my errands done! They also no longer offer the M-F special that made it cheaper than quick lube places. Do they run a better oil blend than the conventional 5W30?