Awwh, really? That's shitty. :/ My connection speed is usually way better, but my ISP randomly decides not to give me even half my regular speed, which is REALLY annoying.. ~_~
Wireless. I plugged my mom's laptop into the modem to check if it was indeed interference, but I still got the same speed, so that's not the problem.. >_>
You should call them and report it. Try to get a idea of when the speed dropped. I used to get huge speeddrops around 22 every night and it turned out to be hardare error on their end.
I was going to call in, but it seems to sort of be fixed now (we're playing together rn, so obviously.. XD). If it does happen again, or I do not get my full speed back, I will definitely call them, though.