Like SeekingZen wrote, breaking down your stuff is a really good idea.
If you're having trouble working for 2-3 hours before going back to the anxiety state, try telling yourself that you have to study for 15 or 20 minutes without thinking of anything else. Usually when I do this, I end up studying for at least 30-35 minutes without even discovering it.
Also, reward yourself when you do good! Eat your favourite cake or play games for some time. Make yourself associate studying with something nice

Good luck, I'm sure you'll make it!