Based on an absolutely brilliant theory someone posted on tumblr about Loki suffering from heat exhaustion during the opening scene of the Avengers and the causes behind it and the rest of his behaviour during the film. So, yeah, this is my new headcanon XD If you want to read the full theory (which I recommend) just go type "Loki heat exhaustion" into google.
Heat. That was all he was really aware of. The burning sensation coursing through body, piercing so deeply into him he was beginning to wish that death would hurry up and free him from the torment.
'Father... help me,' he croaked as the flames blazed around him, twisting the shadows around him into monsters ready to devour him.
A cruel chuckle mingled with the sound of the roaring flames, filling his brain as he tried to focus on the sound.
'Your father won't save you, Trickster. No-one will.'
Thanos watched the God of Mischief as he struggled to fight against the increasing power of the fire around him. His pallid skin glistened with sweat and it was all he could do to keep his eyes open as he tried not to sink into unconsciousness. His emerald eyes were unfocused and dazed as he attempted to locate Thanos.
'Listen to me, Odinson,' Thanos said, finally lowering the flames and striding closer to the broken Jotun. 'You wish for freedom, but freedom is life's great lie. You are no more than a broken doll.'
In a flash, Thanos raised his hand and broke through the ropes that bound Loki to a large rock. The trickster fell to his knees, shaking and gasping for breath.
'In the end, you will always kneel,' Thanos sneered. 'It is in your nature, Frost Giant.'
Loki groaned, trying to push himself up, trying desperately to fight back somehow.
'Does it hurt, Frost Giant?' Thanos asked, with another cruel chuckle.
'What do you want from me?' Loki managed to ask, his voice breaking, his whole body trembling.
'You seek vengeance, do you not? I will tell you how you can get your revenge. Destroy Midgard, let your brother watch his precious Earth crumble before his eyes. I will give you an army to lead, they shall do your bidding, and you shall destroy Midgard.'