It is the stuff of horror movies, where an insect or a giant invasion of insects, or an 'alien' in space gets inside the human body (or in movies such as the 'Mummy' where an Egyptian insect gets inside the skin and cause huge damage); but it apparently happens from time to time. So, for example, doctors have had to do delicate extractions of insects and small creatures from inside the nostrils or the ears where these creatures have climbed inside (typically when the subjects have been sleeping). Now, inside, these creatures are still alive, and movie, giving rise to dreadful feelings in the patient; and it is only in hospital that such conditions are medically cured and the invading insect or creature is removed.
Consider the following case where a cockroach climbed in through the nose, and the lady afflicted, could feel the cockroach moving inside her. She went to one hospital, referred to a second and then a third and finally when a scan was done and then an endoscopic examination, could doctors determine the source of her discomfort. There was something inside her head, and it was moving. Finally the doctors managed to fish inside her head and retrieve the insect (
link to article):
She was soon referred to a second hospital, where doctors suspected she might be suffering from a nasal growth. At a third hospital, doctors recommended a scan, and told her the discomfort may be coming from "a foreign body that seemed to be mobile," The Times of India reported.
Finally, in her fourth doctor visit - at Stanley Medical College Hospital - doctors used an endoscope to find the culprit: a blob with a pair of antennae.
"It was a full grown cockroach," M.N. Shankar, the head of the ear, nose and throat department, told the Times of India. "It was alive. And it didn't seem to want to come out."