I'm feeling unknown fear & anxiety. This must be due to my sins.

Please guide me a spiritual cure for this.

I recommend the following:

1- Every night before you sleep say 100 times La ilaha illa Allah. Don’t say it fast. Take a deep breath and day it.

2- Before you sleep, do Sujud and say “Sobhana rabbial a’la wa behamdeh” for a few minutes. Take a deep breath each time you say it.

3- Take the Qur’an and put it on your heart and recite verse 82 of Sura Israa. It significantly helps.

4- Read this Du’a everyday:

https://www.duas.org/Amn.htm

5- Pray two rak’as and gift the reward of this prayer to Imam Mahdi (a). Then ask him to intercede for you and have Allah help you.

Taking these steps will help you significantly Insha’Allah.