Connection drops and decreasing speeds

Last Sunday I had a day full of connection drops, where the connection would keep dying every so often and losing sync.

As a result, my 16 megabit connection download speed is now just over a quarter of that, stuck at 6 megabits - in the intervening period, the speed had fluctuated between 1 megabit and 8 megabits for the past few days. It's the same with uploads - it was originally 1 megabit and is now back to that, but it has fluctuated wildly and at its lowest was a paltry 370kbps.

How can I make it go back up to its usual speed? And what would cause such a sudden increase/decrease?

Have you done all the usuals ? Router stats as is, then in the test socket of the NTE ? ANy audible noise on the line ?