Grieving is a normal process. However, it can worsen your quality of life and involve more serious symptoms when it lasts for a long time. These symptoms can include:

a powerful pain when you think of your lost loved one
a heightened focus on reminders of your lost loved one
an overall feeling of numbness
a feeling of bitterness when you think about your loss
a loss of purpose or motivation
a loss of trust in friends, family, and acquaintances
an inability to enjoy life

What is complicated grief?

Grief is a normal, expected set of emotions that can occur after the loss of a loved one. However, some people experience a more significant and longer-lasting level of grief. This is known as complicated grief.

Complicated grief may share many of the same symptoms of depression. It can also lead to depression, or worsen depression in someone who already experiences it.

Causes of complicated grief

CG is most commonly caused by the death of someone you love. If your significant other or a close family member dies suddenly, you may have trouble accepting your loss. You may feel intense sadness for years. Your relationships with friends, family, and coworkers may suffer. You may even completely withdraw from your personal and professional life.

CG doesn’t have any identified biological causes. Like depression, it may happen because of:

genetics
body chemistry
personality
your environment

https://www.healthline.com/health/depression/death-loved-one#grief-vs-depression