I have no idea on what might have happened but you can get a list of the built-in keyboard commands by running the following line of vba code which produces a new document containing all the keyboard shortcuts in a table. You can then paste this table into Excel and filter out the blanks in the key column to see all the possible keyboard shortcuts. There is over 250 to choose from.
Code:
Application.ListCommands ListAllCommands:=True
You may discover that keys around the intended keys got hit unintentionally. For example Ctrl+A then any key would replace your content with a single letter. If you then followed it with Ctrl+S then you just saved the doc with the removed content.
It can also be easy to hit the wrong key when going for Ctrl. Different keyboards put Ctrl in different places and your little finger can hit Fn or Alt or Windows key when reaching for the actual key.
You could also have had custom keyboard actions running macros depending on which templates or addins were running at the time.