Signs of rapidly progressing heatstroke include:
- Unconsciousness for longer than a few seconds.
- Convulsion (seizure).
- Signs of moderate to severe difficulty breathing.
- A rectal temperature over 104°F (40°C) after exposure to a hot environment.
- Confusion, severe restlessness, or anxiety.
- Fast heart rate.
- Sweating that may be heavy or may have stopped.
- Skin that may be red, hot, and dry, even in the armpits.
- Severe vomiting and diarrhea.