My iMac (mid 2011) keeps restarting after installing os Mavericks?

I feel like its getting too hot maybe, but lately its been running really slowly and if it gets too slow it will just turn itself off

This is the error code I'm getting when i click on the report after it restarts

panic(cpu 1 caller 0xffffff800e9ebe52): assertion failed: total_sbmb_cnt > 0, file: /SourceCache/xnu/xnu-2422.1.72/bsd/kern/

How can I stop it doing this, or make it happen less often? (It happens at lest 2 or 3 times a week at the moment, with everyday usage)

Cheers