Windows 7: Dramatic download speed change

Hi.
Before I begin let me tell everyone that my download speed is terrible, so please no laughing etc. lol. :P
A few days ago my download speed increased dramatically. I was told by my ISP a few months ago that because of the old lines in my neighbourhood that the maximum speed I could reach was ~1.2mbps but a few days ago my download speed increased to ~4mbps. I took advantage of it while I could and downloaded a few movies and albums but now it has dropped dramatically to ~0.6mbps and I have no clue why.
Any help would be much appreciated as my internet is now extremely slow and even though it was only for a short period, I miss my good download speeds.
Thanks

couple of things, your isp could be throttling your line due to unusual activity. if they are working on the line trying out various fixes you may see an improvement in time.
Main thing is get onto them and ask what is going on, (dont tell them you were downloading)

Raz