According to [Star Wars: Episode III](https://www.youtube.com/watch?v=ohsLZxQYBk8&feature=youtu.be&t=47)

> 
> **MEDICAL DROID:** ***Medically, she is completely healthy. For reasons we can't explain, we are losing her.***
> 
> 
> **OBI-WAN:** *She's dying?*
> 
> 
> **MEDICAL DROID:** ***We don't know why. She has lost the will to live.** We need to operate quickly if we are to save the babies.*
> 
> 
> [Revenge of the Sith : Script](https://www.imsdb.com/scripts/Star-Wars-Revenge-of-the-Sith.html)
> 
> 
> 

Medically healthy humans don't die for no good reason.

**So what did Padmé die of, and how did they even know she was dying?**