Webserver random slow down, 1 hr reboot

Hey guys. Weird issue with a customers server. To start, I do a lot of small businesses administration but don't often deal with webservers so I am a bit stuck. A t320 with whm and 6 or so cpanel accounts w/ websites. php, mysql, apache, as well as the other services that come with whm. 2 nights ago the webserver sent an alert for high usage. Websites extremely slow, TTFB is around 12 seconds. Talked to database admin who confirmed querys were fast, yet mysql using a lot of resources. disabling mysql made no difference in website speed. Pages in the website that make no database calls and are html are very fast, but pages in php with OR without database calls are slow and have the same symptom. This was all of a sudden, website was lightning fast the day before and almost unusable the next. Backups are also failing because of read timeouts, yet there is very little load on the drives. After troubleshooting for a while we rebooted which took over 1hr. iDRAC shows no problems with hardware, further confirmed by another tech currently assisting. Thinking it may be php related? Help!