Server 2008 R2 slow for days...now fine.

Server 2008 R2 slow for 7 days...now back to normal.  Any thoughts?  I've been accessing the server at a crawl since last week.  Restarted it and ran maintenance and performed Windows Updates, cleared temp files, moved Timeslips off of it, paused online backup, ran virus checks.  It became fairly useable over the weekend, but not normal speed.  Today it is perfect again.  Any thoughts?  It never failed or became inaccessible remotely, but it became nearly unusable because of extremely long response times and waits for file shares.  Now it's as if nothing happened.  If users hadn't complained and I hadn't been watching it with one eye for a week, I wouldn't even know anything occurred.