Sin can have mental and physical side effects.

¹ Lord, do not rebuke me in your anger
    or discipline me in your wrath.
² Your arrows have pierced me,
    and your hand has come down on me.
³ Because of your wrath there is no health in my body;
    there is no soundness in my bones because of my sin.
⁴ My guilt has overwhelmed me
    like a burden too heavy to bear.

When you repent from sin, God promises to forgive. He delivers you from sin’s eternal consequences, but he does not promise to undo all of sin’s earthly consequences.