User blog comment:FairyRaven/Fairy Tail Chapter 400: Wings of Hope, Review and Commentary/@comment-9595671-20140913110701

For Sting and Rogue, many their dragons did something so they "thought" they killed them. If Igneel could use telepathy, then maybe Skiadrum and Weisslogia did something while Sting and Rogue were asleep so they'd sleep long enough to think a day passed and they were forced to kill their dragons.

It is a stretch, but its the best way they can be feeling it and also have their dragons inside I can think of.