Nero was struck with a wave of mild nausea. Although he had stamina to spare and was not at his physical limits, expending too much aether too quickly still affected him negatively. This was something he and every other Neophyte would have to live with until they became Initiates. It wasn't even that he was close to expending all his aether. He had been very careful not to do that. But even so, using up a large amount of aether quickly still negatively impacted him.
But the nausea quickly passed, though he still had body aches across his body. It would take some time to recover from that, especially since he was still using his aether to keep the flames outside going. He was hoping that the berserkers would remain in his cryoflames long enough to be affected by it, especially since the machine was still out there fighting them.