We had the same problem with DD (now 2.2)which started at Christmas, after about 3 weeks of no accidents at all.
We tried the getting cross and explaining that wees must go in the potty approach, but that didn't seem to work. We even had poos in pants which was unheard of since aged 10 months! She wouldn't usually let the whole wee out, she would dampen her pants. It was like you say, as if she'd forgotten to pick up on the signals that she needed to go.
In the end, I am sorry to say, we introduced her to smarties! She is much better at her colours now as a result!. Not sure if this was what worked but I think getting cross wasn't the answer. She was also a bit constipated and we got some lactulose from the docs for that, which seemed to help.
In the end, we decided to keep calm, encourage her to go more often, give loads of praise and keep on top of the washing, and it is so nice to be back to where we were- only 1 pair of pants a day rather than up to 5 or 6 pairs!
It took about 6 weeks to get through this, but we got there in the end. Good luck. I have heard it is very common to have a relapse but you just have to go back to first principles (take them often, praise, reward etc).