A computer acting more strangely than usual

I set the computer into sleep mode when I had to go out, so that I could take up typing the email I was part way through later. But, when I came to start using it again, pressing the power button made no difference.

So, I switched off the output of the UPS until the blue light stopped flashing, then switched it back on again and hit the computer's power switch.

It returned to the state it had been in before I set it in sleep mode, half-written email and all. Not that I am complaining, but I wish I knew how that happened. Could it have anything to do with having upgraded to a solid state drive recently?