Link spends seven years in the sacred realm. SOMETHING is happening in there. Perhaps an adventure we've yet to play, or perhaps an adventure that we know and love but has eluded us in it's mystery. Of course I'm talking about Majora's Mask. What I'm saying is, the seven years Link spends in the sacred realm
is Majora's Mask.
Here's what happens: when Link pulls the sword from the pedestal, he enters an alternate reality, a reality in his mind (just like the Silent Realm from Skyward Sword). Link still believes he is living in the real world. He travels through Hyrule as he would if it was real. He borrows Epona in his search for Navi. He makes an adventure through the Lost Woods, but the adventure is in his mind. He ends up in a place that doesn't really exist, Termina. All of the characters in the world are simply figments of his imagination, of memories of his adventures in Hyrule. If you've played Link's Awakening you'd know this is absolutely possible. This adventure is a test of his courage (again, just like the Silent Realm) to see if he is worthy of wielding the Master Sword. As you know in Majora's Mask there are two possibilities. 1. The moon hits the ground and destroys Termina. In this situation Link would be proved unworthy of wielding the Master Sword. He would wake up from the Sacred Realm, unable to wield the Master Sword.
This would cause the Downfall Timeline. 2. Link defeats Majora and proves his worth by returning the Happy Mask Salesman's
precious mask. Link awakens wielding the Master Sword and
continues his journey through the Adult Timeline as expected.
Have any of you ever messed around with Majora's Mask? You know, the 4th day glitch? Then you've probably seen the bone-chilling scene where Skull Kid, Happy Mask Salesman, and Epona (who by the way is supposed to be dead) are simply standing there. Happy Mask Salesman's eyes follow you..

This is the scene where it is all revealed. The journey is a figment of Link's imagination. Epona stands there calmly, Skull Kid and HMS stand there calmly, it is all in Link's mind.
Some of you may know that Majora's Mask was originally intended to have
seven days. One day for every year in the Sacred Realm. Why Nintendo never went through with the other three days or the scene that reveals the truth of the journey, I don't know (ahem, BEN...)
Anyways that's my idea, take a minute to let it resonate.