feel blue
To feel sad, somber, or glum. I have been feeling blue lately, but I think it's just because of this gloomy weather we've been having.
feel blue
Fig. to feel sad. You look like you feel blue. What's wrong?
feel blue
Be depressed or sad, as in I was really feeling blue after she told me she was leaving. The use of blue to mean "sad" dates from the late 1300s. See also blue funk, def. 2; have the blues.