Notice which day of the week you always feel worst. Patterns are clues, not character flaws.

A low that arrives on schedule is information about the schedule. If Sunday evening is reliably the worst part of your week, that is not a fact about your personality; it is about what Sunday evening contains, which is usually a week’s worth of unfinished things arriving at once. Patterns point at causes, and causes can be moved.

So find your day, then find what is in it. Look at sleep, food, who you see, what is due the next morning, how much was left to the last minute. Change one and watch the same day next week, which beats blaming yourself for the feeling.