Gail are you wireless ??
Or do you have a cable into your router?
If your wireless it can be a hundred things causing the
sigal to drop, ie Baby
monitors, mobile phones...
Best advice is to monitor it over a few days
before you start to panic
It can also depend upon the speed tester program,
as in where is it in the world etc..
3804.69 Kbps = me with a torrent running with a cable (8mb Sky)
1751.32 Kbps = Gail (8mb Sky)
i suspect your wireless and thats why?