My dad always referred (humorously) to “that feeling of impending doom.” As an adult, I’ve learned that he wasn’t always being funny.
For me, the worst is that nagging and persistent feeling that you’ve forgotten something critical. It’s usually the worst about 23:30 on Sunday night, when I just know that there’s something that I was supposed to do this weekend and I’ve completely forgotten about it.
Then I realize that it’s just my subconscious reminding me that it’s “Monday Eve.” So, yes, I almost certainly have forgotten something critical, but that’s okay. It will get lost in the details of a Monday.
This, however, does not necessarily make me feel better.