Plate Coral

[iFish]

I bought a plate coral on Sat. It was about the size of 1/2 a baseball, but this morning, it had swelled to 2x its normal size. (I had left the lights of for 24 hours because of heat - I had to run the aquarium without a chiller for a day) I turned the lights on (I have 130 watts of PC lighting Acintic/Daylight) and it began to get noraml sized again. What happened? Is it bad? (I think so )