Sudden High CPU Usage On SQL Server 2008R2
Answer converted from comment:

sp_whoisactive shows the following output:



Restarting the SQL Server Service resolved the issue. I think I know why thanks to sp_whoisactive. My theory is we have a query that was running in a loop (the top 8 rows) and that got stuck during the DBCC DBREINDEX that occurred at 12:30AM. This query was using up all of the CPU since it was stuck in that query... Once the server was rebooted, there are hardly any records in the sp_whoisactive. MUCH BETTER!!