Can MacBook Pro be used 18 hrs daily? I am using a 13-inch Mid 2012 MacBook Pro that I got about an year ago. I am a writer and work primarily on Word, Safari &amp; Preview. And I work on the machine for an average of about 16-18 hours a day.

It's become slow several times and I have already re-installed the OS twice. I installed Mac OS X 10.9.4 Mavericks after it was released and I upgraded my RAM so that it has 10 GB of RAM instead of the standard 4 GB RAM.

Still the MacBook Pro has become slow again and—more problematically—it has started shutting down without any warning or any notice after re-start.

I cleaned the Mac, reset SMC and increased the free space on it. Still the crashing problem continues.
Sudden shut-downs I would always attribute to heat - dust/fluff collecting in the fans &amp; heat sink fins. It takes more than a quick run-round with a duster or a can of air to properly clean out the fins; it needs splitting open &amp; getting in properly - even so far as replacing the heat sink paste.
It's not a job for a beginner, especially on a laptop, but the guys at the Genius bar ought to be able to steer you in the right direction.