Preoccupied with depressing, morbid, or painful memories or thoughts: (Dictionary.com)
Cast in subdued light so as to convey a somewhat threatening atmosphere: (Dictionary.com)
Moodily or sullenly thoughtful or serious. (Merriam – Webster)
Darkly somber. (Merriam – Webster)
Making you feel uncomfortable or worried, as if something bad is going to happen. (Cambridge Dictionary)
Feeling sad, worried, or angry for a long time. (Cambridge Dictionary)
Engaged in or showing deep thought about something that makes one sad, angry, or worried.
Ten Surprising Reasons You Shouldn’t Brood.
The Brooding Mind: Making the Worst of Ambiguity.