3 year old had seizures out of blue. Then her sister does a week later, whats going on?

A 3yr old girl, had seizures for the first time last week. She was brought to a hospital, and for 5 days given all sorts of tests by a specialist and then diagnosed with epilepsy. The day she comes home her 5 year old sister is acting normal, but seems to be becoming sleepy. She then fell asleep in the pool, which baffled me, but we could wake her up. She had no fever and just seemed tired. She slept the rest of the day even though her mom said she went to bed normally and woke up normally. I couldn't help feeling like something was wrong and it could be related to whatever is wrong with her sister. I thought about her all night long. The next day when she arrived at day care, she had a seizure too. They took her to the hospital, but I don't know the outcome yet. I don't know the family too well, but can't get the children...and their poor distraught mom out of my head.

Is this some strange virus or just a coincidence? Am I watching too many House episodes?

UPDATE: The older brother had one today. We figured out that the three of them all went swimming prior to the episode. The boys incident occured when he fell asleep on the bus ride home from a trip to a waterpark.

Wow that is so odd. I would be worried about something they might be breathing in the house.. They need to get that house tested for EVERYTHING.. Mold, Asbestos, you name it they need to test for it!

Maybe a gas leak in the house, or something else leaking in their home? You would think by now a 5 yr old would have shown signs of epilepsy by now.....I will say a prayer for you & them :)

Are the parents abusing or shaking these children? Sounds like something is going on in that household.

Not everyone who is born with epilepsy shows signs before they are 5. I had my first seizure when I was 9 months old and that's considered early. In our family it's hereditary. My brother is turning 18 this year and he may have it as well. Everyone is different.