Check out Image How come ?
But this last for only 2 Hr
then again at normal speed of 2-10 KBps
Using Net Limiter
Spikes happen sometimes, its normal 
2years ago my bsnl dataone broadband with home 500 plan normally has 200kBps speed.
it was hovering between 500-700kBps happened one night 2 yrs ago
spikes do happen sometime
Spikes on Broadband are usual alright (since the modems are not capped in case of DSL…and the speed is controlled at the DSLAM , but it is not the case with 56K modems which are supposed to provide a max data rate of 56kbps~~ 7 KBPS… so it is not at all normal if you ask me…
Yep myself exp. this somedays back i download on avr. 3GB daily but i dont know what happened on one night i downl. 15.090GB 
15 GB WOW !!! Now Ia m on BSNL NightUL Plan I can download max 4.5 GB regulearly 3.7 - 4 GB
It is 4 years old , quite a age to bump