I had that feeling too, I don’t have it anymore though and I’m perfectly fine and well. There could be an underlying mental or physical issue. You could talk about it with someone you trust and hearing from them that you’re just fine could subconsciously affect you more positively. Also, hearing similar rational affirmations about yourself from someone else will only strengthen your rational thoughts on the matter, instead of desensitising yourself by telling yourself those same things over and over again. You’ll probably be fine if you’re doing great healthwise.