Well, it manifested itself in the form of the child. Which makes no sense at all when you could've had the dead Virmire squadmate be it (if you listen to the child talking there is another voice in the background, probably the Reaper god or whoever).Also Shepard has been on a goddamn suicide mission; how is he getting PTSD seeing some random child die.
Then again that child turned out to be an omnipotent space wizard.
Yeah, the PTSD dreams kinda sucked because Ash/Kaidan wasn't in them or if you lost anyone in ME2 or even possibly flashbacks from your psych profile (colonist, sole survior come to mind) either. A damn kid.