Seemingly impossible events, such as an icon weeping or the sun pulsating in the sky, have yielded to explanations of fraud and people's retinas reacting to staring at an intense light. These types of miracles turned out not to be what they were built up to be. On the other hand, a few years ago, a policeman woke up from a several year coma. As truly unusual as this situation was, being in a coma is not the same as being diagnosed brain dead. People can wake up from a coma.
Brain death is very different.
No one ever properly diagnosed as being brain dead has ever woken up from this state. That would be a supernatural miracle. It seems that for the general public, there are only two crucial elements which make an event a miracle. These are that the event be beneficial and it be extremely unlikely. Under these terms, I would readily admit that miracles happen all the time.