Breathlessness is not normal, therefore it should be checked out, espescially in someone elderly. There are a many possible causes, the majority of them are of no great concern but a few are and the earlier they are disanosed and treated the better.
Temporary breathlessness, espescially with other chest infection telltale signs such as a productive cough or preceded by a temperature and in someone young, it is safe to ignore it unless it goes on for weeks.
Breathlessness, espescially at rest, in someone elderly with no other obvious signs is more worrying, particularly as the incidences of more serious causes rises with age.
It might not even be a problem with the lungs themselves, for example, many heart conditions also lead to breathlessness because the flow of blood is inadequate, the body detects the lack of oxygen and stimulates the breathing to try and increase the supply.
It is espescially important to refer to a doctor if it continues for three weeks or more or shows signs of progressing.
It could easily be the heat - this throws a heavy load onto the body and organs like the heart - but only a doctor can tell.