For example, having had long standing plans to attend a late night event, I suddenly realized that I was really tired and it will not be a good idea to attend. While I made the decision to not attend the event, I was filled with regret, despite still being able to attend despite being tired.
I usually understand regret is a feeling about something that happened in the past.
What would you call a feeling that happens about something that is about to happen in the future, where you in theory can avoid it, although perhaps not in practice (since there was some reason to avoid it).