star wars - What did Padmé die of?

According to Star Wars: Episode III

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}}

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?

Answer

Medically healthy humans don't die for no good reason

But she wasn't "medically healthy".

She was suffering from - at the very least:

1. 
   

   Twin birth. That's a pretty stressful thing to happen to a human body, especially if it was premature, possibly caused by, or at least correllated with ...

   
   



2. 
   

   Injuries from Anakin force-choking her in a fit of jealous rage. She was unconscious at the end of it (when you lose consciousness, it can indicate Bad Things are happening in your brain):

   
   

   

   
   


3. 
   

   Also, psychosomatic effects from pure psychological shock does have a capacity to cause major physiological issues.

   
   


4. 
   

   To top that off, we don't know what the exact state of medical science/technology in TGFFA is. For all we know, they don't know how to help someone who's in cardiac arrest - meaning a heart attack could be written off as "broken heart, can't help here". Or, more likely, an aneurism (I didn't notice them scanning her brain at all).

   
   

   Remember, you (well your question) just trusted the opinion of a medical droid that declared a woman who just gave birth to twins a clean medical bill of health.

   
   
   

   Having said that, canon simply doesn't give an unambigous answer that would be scientifically plausible, anymore than it cares about lasers and ion engines making sounds in a vacuum, or the ability of midichlorians to somehow cause a virgin birth in absence of DNA from a male reproductive cell in a species emphathically NOT designed to work that way. So,

   
   


5. 
   

   Complications from severe plot failure. She died of Lucas writing the scenario.