dead in an hour??

Question
Hi Christy, I just have some questions.
IS IT POSSIBLE FOR 4 FANCY GUPPIES TO DIE WITHIN AN HOUR?
:(:(:(:(:(
I cycled my 5 gal and put the fish in, afterwards, my dog was bugging me to go out. So after inspecting each fish, (which by the way, looked healthy) I went out with my dog.
I usually go for an hour or so, when I came back, all I had on my mind were the guppies, I raced upstairs and came into the tank's room. When I looked inside the tank, I found one guppy stuck to the filter, motionless, one guppy belly up, one guppy dead on the gravel and one caught in a plant. I looked at the fish before scooping them out and saw holes in their heads. I was so freaked out , those weren't there when I left them.
what happened?
Thanks!

Answer
Hi Danny
Yes, it's possible.  Initially while I was reading your question, I was thinking they were some how poisoned, maybe through chlorine in the water, or something else that accidentally got into the tank.  Then you threw in there they had holes in their head....Honestly, I have no idea what would've done that nor have I ever heard of that happening, aside from hole in the head disease that's common to oscars.  But that's a progressive disease, and doesn't just appear within a few hours like that.
What size are the holes?
What else is in the tank, any live plants?

Christy