I can skip between worlds

Aaron is a normal high school 2nd year student with a very normal life. One day when he is returning home from school, he meets an accident,....almost. He returns home thinking that he was very lucky that he was safe. But when he enters his room, he slips on a banana peel that he had carelessly tossed the same morning and hits his head on the doorknob. He looses his consciousness and when he regains it, there is an old man in front of him who calls himself GOD.

God allows him to reincarnate in another world of his choice with a unique ability that he wants. He chooses a world and ability that he likes and starts his adventure in the new world. But soon he feels sleepy so he goes to sleep. But immediately he wakes up in his room, his head still hurting from being hit. Did he just dream or was it a reality? Or did he just develop multiple personalities??