Uptime shows the average usage in the last 1, 5, and 15 minutes.
If statistics weren't being kept in the past, I doubt you can find that the problem was before rebooting, unless some error message was logged.
You might look in /var/log/messages to see where the last messages came from.
You could run top in batch mode and redirect the output to a file. Other common tools include vmstat, procinfo, mpstat & oprofile (opcontrol/opreport).
You might want to monitor and log the performance statistics over a certain test period of time in the future. Some of the tools, like vmstat can suppress the headers so that the data can be loaded into a spreadsheet.
Last edited by jschiwal; 02-01-2007 at 09:09 PM.