Extreme emotional swings.
Unstable emotions and moods are common with BPD. One moment, you may feel happy, and the next, despondent. Little things that other people brush off can send you into an emotional tailspin. These mood swings are intense, but they tend to pass fairly quickly (unlike the emotional swings of depression or bipolar disorder), usually lasting just a few minutes or hours.HelpGuide.org
Intense and highly changeable moods, with each episode lasting from a few hours to a few days.NIMH
Wide mood swings lasting from a few hours to a few days, which can include intense happiness, irritability, shame or anxiety.Mayo Clinic
Periods of intense depressed mood, irritability or anxiety lasting a few hours to a few days.NAMI
This is one of nine traits used to diagnose borderline personality disorder. Many are common to other disorders, and you should seek professional guidance (if accessible) if you are concerned about a diagnosis.