That has happened to some people, not really sure what the problem is. Make sure you have all your updates I guess. Try shutting it off and pulling the battery for a little bit then put it back in, see if that helps.

 

I know its been happening to me in the last day as well

 

Try a reboot, and also look into any apps or widgets you installed recently. When I first got my phone I installed the widget that makes an icon for hte web browser that looks ilke the chrome logo, and I got sense FC's multiple times per day until I removed it.

 

Might try Menu > Settings > Applications > Manage Applications > All Tab > Press HTC Sense > Clear Data (and cache if available)

Now reboot for good measure.

May have to set up your homescreens again but if it works, it's better than FC's which suck.