Each night on of my kittens (4 months old) is vomiting. It is just one single spew of very well digested food/liquid about the size of a 10p. She is not ill, no diarrhoea, plays well, is happy and purry. It only ever happens at night, only once and at about 5am. As far as I am aware this kitten only eats wet food which is long gone by that time of the morning. I wondered if it could it be the result of an 'acid tummy' due to hunger?