Your personality can gradually change throughout your life. Fluctuations in mood from time to time are normal. However, unusual personality changes may be a sign of a medical or mental disorder.

A personality change can be demonstrated in a variety of ways.

For example, a behavior that’s inconsistent with how you would typically react under said circumstances indicates a personality change.

A person behaving in an uncharacteristically moody, aggressive, or euphoric manner, inconsistent with their usual way of behaving in similar situations also demonstrates a personality change.

Causes of personality changes
Grief, bad news, and disappointment can cause a normally happy person to become downtrodden. Sometimes, a person’s mood can be altered for weeks or months after hearing devastating news. However, mood changes aren’t the same as personality changes.

However, some people experience unusual or strange behavior for years, which may occur due to an illness or injury. A person may experience a change in their demeanor after experiencing a traumatic situation or witnesses an unpleasant event.

These behavioral changes may be caused by a mental health condition, such as:

Anxiety: Anxiety occurs when a person feels nervous or uneasy about a situation. It’s normal to experience some anxiety, but when it occurs on a regular basis without provocation, it may be a sign of generalized anxiety disorder.
Panic attacks: Panic attacks are periods of extreme fear. Sometimes, the fear seems to be irrational. Such situations include a person having a panic attack when seeing an elevator or speaking in public.

Post-traumatic stress disorder: Also called PTSD, this is a mental health condition marked by extreme fear, flashbacks, and in some cases, hallucinations. PTSD is triggered by memories of trauma, such as a terrorist attack or car accident.

Bipolar disorder: Bipolar disorder causes a person to have extreme fluctuations in mood. Mood changes can include euphoria and extreme depression and may alter the way a person responds to certain interactions or situations, depending on their mood state.
Schizophrenia:Schizophrenia makes it difficult to think clearly, to effectively comprehend situations, to behave as normally in social situations, and to distinguish between what is and isn’t real.
Medical conditions that cause a fluctuation in hormone levels can also cause strange or unusual behavior. These conditions include:

menopause
premenstrual syndrome (PMS)
andropause (male menopause)
hyperthyroidism or hypothyroidism (an overactive or underactive thyroid gland, respectively)
Medical emergencies can also cause strange or unusual behavior. These situations include:

heart attack
stroke
dehydration
malnutrition