Heart stopping moments - was I losing Windows 8?

A panic tonight - but with a happy ending so far - but it made me very nervous. I turned on my W8 computer (HP Touchsmart with i5/6GB RAM/2TB HDD/ separate graphics card), and it started to give me a series of messages along the lines of "Preparing for first use - installing drivers - installing apps - almost there etc - all against an ever changing W8 series of backgrounds. In fact, exactly the same as it did (quite correctly) when I installed W8 three months ago. Then the screen went blank, and all that was visible was a mouse pointer that I could move. After an agonized wait, I shut the computer down by holding down the power button. It politely told me "Shutting down". I then turned it on again, and W8 loaded quickly and correctly with no delays or messages, and all programs, documents etc were exactly as I had left them yesterday. What happened - why did the computer give every indications that it was starting from scratch? As an aside, I downloaded quite a lot of W8 updates a couple of days ago, but had used the computer since then. Any thoughts - not sure my blood pressure can stand this again !! Thanks in anticipation.