From ep 11.23
Cas: Sam, I'm so sorry. If you need to talk... I'm here if you need anything.
It links with this earlier scene...
Dean: Listen, if... when this works, Sam's gonna be a mess. So, look after him. Make sure he doesn't do anything stupid.
So, here we have Cas looking after Sam, and then Cas gets zapped away. Sam gets a gun pointed at him, he throws caution to the wind, and he keeps walking towards it. A little suicidally reckless...
edits by me