I also think this reflects water damage which is often described as oedoma. This happens as the plant takes up water too quickly and pressure causes ruptures in the leaf tissue which look like blisters"

"Oedema may occur when plants have been over-watered during periods of high humidity. It can also occur when soil is moist and air is also moist or cool. These conditions are most likely to occur with houseplants indoors in late winter or early spring, especially during cloudy weather. Such conditions allow water to be absorbed by the plant but lost only slowly by means of normal transpiration through the leaf surface. Occasionally oedema does appear on plants that have been kept relatively dry and have grown under conditions of low humidity."
-----http://www.extension.umn.edu/garden/y...

Your plant will recover. Just avoid overwatering