The Odinsleep is a state of deep sleep where Odin recharges the Odinforce (a magical force that gives Odin his power) and is left as vulnerable during the process. Odin is also completely aware of his surroundings and what is occurring throughout the universe, from Asgard to Midgard in his Odinsleep.
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After Loki angrily berated his adoptive father about not informing him of his true nature, Odin collapsed in shock. Immediately after, Loki called upon some guards to help, they then carried him to his bed chamber where he is supposed to stay until his Odinsleep is over.
Not long after, Frigga visited Odin's bedside while he was still in the Odinsleep with her adoptive son still present. When Thor found Mjølnir on Earth, but failed to claim it, he was killed on Earth by the Destroyer. Odin sensed this and a tear fell from his eye.
Later, Laufey tried to kill Odin as a part of Loki's plot, but was double crossed and was killed as a result. During Thor's battle with Loki on the Rainbow Bridge, Odin woke from the Odinsleep and tried to save them from both falling off into the abyss but lost Loki, who chose to let go, falling into a wormhole.