why they were tired

I was back from the swimming pool and my friend was tired. How could she be because we had lunch and a break before we left. something was definitely going on but what.A few minutes later I asked my mum for a snack, she was too tired so I asked my friend to get us our water bottles but she was to tired. I asked them both to go away so I could find out what was going on but they were exhausted. Was this a contagious illness how would I know. I wanted to know immediately but how...