I speak this from personal experience: I had suffered from a disease called Ankylosing Spondylitis. It had affected my hip joints making it difficult to move them. One day, while in a church service, I was healed. It was an experience that I felt as much as believed.
I was able to walk out the church without crutches. An hour later, after being plagued by many thoughts and doubts, I was again unable to walk without crutches. So I know from experience that a man can receive healing and then lose it when his faith fails.
Was there medical proof of my healing? No. But there was visible proof - my walking.