Cannot wake my Remote Mac for Screen Sharing

This keeps happening and I suspect it is just sleeping, but why it wakes sometimes and not others is the mystery.

Here is an examplr from this morning. I accessed the computer remotely with no problem at around 9AM. This after not having been there for accessing remotely for about 7 days. If if it was ever asleep… it would have been this morning.

So I got distracted before I could finish what I was doing the session expired becuase my local machine went to sleep and now at 11:30AM it will not connect to the same machine at all. Last time this happened I got someone to pop in and it seemed to be frozen (although, not sure as the person is not at all savvy in computers).

Why would the machine after a week be available and then not after connecting once. And why (if this is what is happening) might it freeze when using screen sharing?