I'm very sorry you lost your two hammies
Pets at Home aren't the most ethical breeders, so the hammies there often do have quite a bad start to life.
My first thought when reading this was a diet-related issue! I'm sure this is none of your fault, but were you feeding Chichi and Jango the same food (from the same bag) and did you recently open a new bag? What food did they have? It could have been a batch problem.
As for being more sleepy the last few days, that's likely from a weather change or her just settling into her new home and being more comfortable when you're asleep. If you are concerned, I would take her to a vet.