I have been having this problem for at least a week, as well. Sometimes, I can play for about 30 minutes (maybe longer if I’m really lucky), but then the lagging and the DC’ing happens. And I also can continue to use the chat window.
And to make things even more frustrating (for me), my sister has the exact same computer model, the EXACT same hardware right down to the same USB WiFI wireless adapter, but she’s not affected by any of this (the only difference is that she’s a few feet closer to the gateway). It’s just me.