If you did TOP in ssh, and noticed httpd process has a high cpu load, and has been running for a long time (e.g. over 5 minutes) then you might try lowering your MaxRequestsPerChild.
vi /etc/httpd/conf/extra/httpd-mpm.conf
Now change your MaxRequestsPerChild from 1000 to 20...
<IfModule mpm_prefork_module>
StartServers 5
MinSpareServers 10
MaxSpareServers 20
ServerLimit 812
MaxClients 812
MaxRequestsPerChild 20
</IfModule>
service httpd restart
