Hey, I'd start with the following information it might give you some clues as to what is up or will at least help TAC debug any problems.
Show the current CPU load:
#show cpuload
Show current CPU load based on processes
#show cpuload current
Show the current memory usage
#show memory debug verbose
And to show everything :D
#show tech-support
It might be worth posting a little more about your environment, for example how many users, how many AP's how many firewall sessions you have open? Some of these commands mayt need to be run from the serial port if the CLI is unresponsive. Are you doing any DPI etc? It might be a case that you are reaching the platform limit or a process is causing a CPU spike.