Below is a rather amusing recently discovered account of a young nun in York called Joan of Leeds, who escaped her convent in the early 15th c by pretending to be dead and leaving a fake body in her place.
Many monks and nuns, especially those who had entered a monastic house at a very young age and not by their own free will found themselves unsuitable for the religious life as they grew older. Most of the escapees would vanish to join a prospective lover.
Even royalty sometimes left monasteries under a cloud. Edith, later known as Matilda, the wife of Henry I was in Wilton Abbey for her education, not to become a nun. However, when it came time for her to marry, many insisted that she had taken vows while in the convent and hence was not eligible. Edith was having none of it. To show them she was truly not a nun, she flung her wimple to the ground–and trampled on it.