Could have the effects of heat exhaustion the day after you were outside in 99 degree heat?

It sure can... Depending on the severity of heat exhaustion, your health status, and how quickly you get intervention, the effect may last for several days. Mild exhaustion gets better fast with simply staying in cooler area and replace the fluid lost. Severe case may need hospital care/iv fluid and/or medications. Older folks with medical problems are more prone to heat exhaustion. Consult doc. Good luck.