It's what happens y'know; this guy is just a shit-tier writer.
Viserys gets pissed at being mocked and having to sit at a lower table, when he feels superior to Dany.He gets pissed and starts making demands, while hitting her.Khal Drogo gets pissed and pours molten gold on his head to give him his crown that he spent the whole fucking trip whining about.
This is also when they reach Vaes Dothrak, where Dany does everything right, for a preggers Khaleesi.This witch who was being beaten by the Khal's men that Dany saved earlier offers to heal Drogo, but curses him as revenge. She then offers to save him in exchange for the fetus, and Dany
agrees.It doesn't work, and the baby is lost, Drogo is a vegetable (coma).Dragons hatch and kill the stupid witch, then bond to Dany and start drinking her breast milk.
That's how I remember Dany's story, anyway.