Hamsters died - I had two, both of them died suddenly WHY? HOW?

When I left them at home they were fine... I went out with friends and returned after a few hours and they were both hidden behind their slide, lying one top of another... I gave them a bath and dried them properly 3 days ago, they were well fed and active until the afternoon.. What could it be? was it some health reason or any negativity that they took upon them or what how could they die? they were fine.. a few hours ago...