I think that's because so many people just keep to themselves these days. So, maybe people noticed that you may not be yourself that day, but so many don't want to take the time or just feel they are interfering and should mind their own business.
I think the days of long ago, when people communicated all the time - directly, face-to-face - no text messages or internet, is how things should be. When neighbors would visit each other on the porch and people socialized all through the day. Now we all just keep to ourselves. This makes for a very lonely planet of people.