Weird reboot - should I worry?

On Friday evening I turned on my 2011 iMac running 10.7.5 and it stayed on the grey screen for ages with a progress bar running, the type you get after a firmware update.

Then it asked me to log on, which I never normally have to do when starting my computer.

Then trying to open Chrome using cmnd + space, Spotlight appeared empty of results. I also noticed that Crashplan backup hadn't started automatically, as it always does.

I rebooted the Mac and this time no logon was needed, Spotlight search was populated and everything worked fine.

Any ideas what happened there? Should I be worried?