My bedroom ceiling and walls were skimmed about 6 months ago and have since been painted with a matt emulsion paint (4 coats). I am pleased with the finish but in the last week I have noticed a hairline crack in the ceiling (about 1m long) and 3 hairline cracks on one wall around the light switch. I can't tell if it is the paint that has cracked or the plaster underneath, it looks like just the paint to me, is this possible. Does anyone have any thoughts on how to fix this?