|I think you need to tell us what type of highspeed package you have and what the rated bandwidth is before we can assume there's anything wrong in the first place.|
I know my parents, on my advice, have a "highspeed lite" package with limited bandwidth. If you have a similar package, that could be your 'normal' limit in which case nothing is wrong.
Also, other things that affect rates are the internet itself and the server you're connecting to, or downloading from. If the internet is busy and the same is true for the server, then your rates will drop accordingly.