Mark11:26 But if ye do not forgive, neither will your Father which is in heaven forgive your trespasses.KJV
There are a lot of hurting people in the world today. Psychiatrists can attest to the fact that there are patients in mental institutions who got there as a result of bitterness in their hearts. While I appreciate doctors for their effort to help such people, we should not forget to look at the spiritual side of the issue. From my observation, sometimes, people living with guilt feelings, depression, and those who feel rejected often harbour bitter feelings towards some people in their lives especially those who hurt them in the past.
The poison that unforgiveness injects into our system is called bitterness. Most times, bitterness comes with the feelings of revenge. That's how you know that you're yet to forgive your offenders. The scripture says: "Look after each other so that none of you fails to receive the grace of God. Watch out that no poisonous root of bitterness grows up to trouble you, corrupting many"(Heb12:15 NLT). You cannot stop people from offending you. It would happen till Jesus comes.
By the Spirit of grace available, you can forgive instantly those that offend you. After Jesus breathe on his disciples saying they should receive the holy Spirit in John20:22, the next thing he said was: "If you forgive anyone’s sins, they are forgiven. If you do not forgive them, they are not forgiven”( vs 21). That implies that once you have the Spirit of God in you, the capacity to forgive is in you already. You need to make a conscious decision to let go and allow the Spirit help you against bitterness. Take your hurtful feelings to God. If you forgive, you'll be helping yourself to be free from the poison of bitterness.
Take all your hurts to God in prayers and ask for grace to forgive all your offenders. When you do that, the journey to emotional healing would begin.