Check the modem logs.
There is an ongoing problem in my (very) local area causing random disconnections for random periods of time. The upstream power level is pretty unstable fluctuating from 45 up to 58 over a given period of time. When it goes beyond 58 (as I understand it) the network will (in slight different words!) tell the modem to get stuffed - triggering a reboot of modem and dead connection until it recovers.
The tech was escalating it last week after getting sick of going to the same 4 houses every week for the same fault - but I've had the same problems again this morning so it looks like networks have done their usual
Edit: Just noticed the time you posted - it's also possible there was some last minute maintenance going on before the Christmas network freeze and there is nothing actually wrong with you're connection
