I do hope your bird recovered. Any time a bird shows signs of illness, it is best to take it to an Avian Vet as soon as possible. Your bird may have been suffering from heat stroke or possibly some airborne toxin, however in the second case, both birds would have been affected. If these are normally inside birds, then the temperature change may have been too extreme. Birds need gradual temperature changes, so unless the outside temperature is very mild and about the same as indoors, it is not a good idea to put an indoor bird outside. I know many bird owners want their birds to have fresh air, but there is a greater risk to their health if they get too hot or too cold.
When a bird is overheated, misting it lightly with water can help. With a tame bird, you can also tuck wet cotton balls under the wings, against the body. An overheated bird will pant like a dog and hold its wings away from its body. A fan directly on it is not the best thing because it can cool the bird down too quickly, and drafts are not good for birds.
Again, I hope everything turned out good.