According to the National Institute of Mental Health (NIMH), bipolar disorder, aka manic-depressive illness, is a brain disorder that causes unusual and dramatic shifts in mood, energy, activity levels, ranging from high-highs and low-lows. This mental instability can make it difficult for an individual to carry out day-to-day tasks.

While bipolar disorder is not common—less than 3 percent of the population experience it every year and 4.4 percent in their lifetime—over 80 percent of cases are classified as “severe.” If untreated, bipolar disorder often worsens, and can have an ultimately devastating impact on an individual’s life.

Unsure what qualifies as bipolar symptoms? Here are 13 signs that your or a loved ones' mood issues may actually signal bipolar disorder.