I know, I know... theories about the prequels (trying to make them tolerable), but this one makes too much sense (to me) not to share.
I was reading one of Ina May Gaskin's midwifery books (this one from the late 70s), and something clicked when I was reading about toxemia. It's a complication in pregnancy that doctors aren't really sure about the cause. Most sufferers are young women, with their first pregnancy. It's more common in multiple pregnancies.
This is what really killed Padme. Not a broken heart.
Need convincing? Toxemia has two parts: pre- eclampsia and eclampsia. The symptoms include severe headache, severe nausea, nervous irritability, visual disturbance, and pain in the upper abdomen. It can be fatal. Eclampsia comes on suddenly, and the woman may die of shock, convulsions, or edema in the lungs. Sometimes labor has to be induced to avoid that, and even today it can turn into a save the baby, or save the mother scenario, although it can be prevented with prenatal care like special diets, bed-rest, and other measures to ensure proper circulation.
It's probably a given that Padme had little to no prenatal care (she was probably afraid to seek it out), and she couldn't very well have taken bed rest. The fact that pre-eclampsia can mess with your head would explain some of her changes in personality, as well as dealing with the physical symptoms. And it explains her sudden death a whole hell of a lot better than "she lost the will to live."