Can the cause of intense sadness and depression, fear of speaking with people, and doubt in the acceptance of supplication and prayer, be due to negligence in performing the Fajr prayer on time?

We congratulate you on your repentance and advise you to preserve it by turning to Allah and frequently remembering Him. As for the symptoms you are experiencing, they stem from several reasons, including:

1. Isolation: After guidance, you must choose righteous company that will aid you, replacing your old companions with them, as Allah says: (And keep yourself patient with those who call upon their Lord morning and evening, seeking His countenance. And let not your eyes pass beyond them, desiring the adornments of the worldly life. And do not obey one whose heart We have made heedless of Our remembrance and who follows his [own] desire and whose affair is ever [in] neglect.) Al-Kahf/28. 2. Remembering the past: This is natural at the beginning of the path, and the whispers of Satan disappear with steadfastness on guidance. 3. Doubts and obsessions: These are from the whispers of devils; you must repel them by seeking refuge [in Allah] and supplicating to Allah to strengthen you. 4. Neglecting Fajr prayer: This is a significant deficiency. The Prophet, peace and blessings be upon him, said: (Whoever prays the morning prayer is under the protection of Allah; so let Allah not demand anything from you regarding His protection, for whoever He demands something from regarding His protection, He will overtake him, then cast him on his face into the Fire of Hell.) Narrated by Muslim (657). Correcting this neglect is essential so that you are not deprived of Allah's protection and security.