Mine has a tendancy to do that, more often than not in winter though, when the nights get longer. Despite wanting to keep it at 8128, exchange congestion is generally the bottleneck, so losing upto a meg of sync harldy makes a difference.
If you post your full stats (attenuation/SNR etc.) then someone will be able to figure out what's going on. I suspect a series of disconnections at some point (thunderstorm, voice fault maybe) has pushed your target SNR up from the default of 6db. Mine can't handle 8128 at 9db or higher.
My stats, for reference:
ADSL Link Downstream Upstream
Connection Speed 8128 kbps 448 kbps
Line Attenuation 31 db 7.5 db
Noise Margin 7 db 27 db