For some, summertime is anything but sweet.

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What is supposed to be the most relaxed season of the year comes with triggers such as schedule stress, Instagram envy (is everyone else on vacation?) and a hatred of the heat.

Oftentimes, these feelings are little more than in-the-moment frustrations. But in some individuals, seasonal upset is actually summer-onset seasonal affective disorder, or diagnosable summer depression.

"Having seasonal depression in the summer is not as common as wintertime depression, but mental health professionals do see it," Michelle Riba, M.D., a clinical professor of psychiatry at the University of Michigan and associate director of the U-M Depression Center, said last year.

"For people who have been diagnosed with bipolar disorder, manic episodes often peak in spring and summertime," she added.

If this sounds familiar, consider these signs and symptoms of summer depression. If you have concerns about these symptoms or any others, talk to your doctor: Depression is treatable, whether through talk therapy, medication or other means.

Other depression symptoms (year-round) include:

• Feelings of hopelessness and pessimism, or guilt or worthlessness

• Thoughts of death or suicide

• Difficulty concentrating, remembering and making decisions.

Sources: NormanRosenthal.com, the Anxiety and Depression Association of America and the Mayo Clinic.

If you've been newly diagnosed with depression, visit Michigan Medicine's Depression Toolkit. For more information, visit the Depression Center online.