As far as I'm aware, for the first 10 days your line is in its training period so you should expect to see it sync at different rates. In a nutshell, something caused your connection to drop, and when it re-connected, around 33k was the best sync rate. This in turn made bt's DLM dropp your profile to 33k.
best course of action would be to restart your modem and router during off-peak hours to get a better sync rate. After that your ip profile should rise within 5 days, depending on the % increase.