Sorry for the delay.
If you haven't backed up your data, it's a good idea in case the problem gets worse.
Anyway, you may want to check your power management settings to check if your hibernate, standby, or 'turn off hard drive' settings are set for 30 minutes and disable them to see if that stops the problem.
I'm a little worried there could be something wrong with your hard drive although it's unusual if that is the only time you see problems using it.
