A world that just disappeared

I don´t know if the new minecraft in XBOX ONE is bedrock or not, but the problem is that two worlds have disappeared. The first time I disconnected of a world when I was in the Nether and the next time I tried to enter the world, its miniature was in black, and I couldn´t enter to it. Today is the first time I can enter since that happened.  The second world has just dissapeared, yesterday it was fine, but today it´s just gone, I think it may be in the cloud, but it makes no sense that i can´t see it...moreover, I didn´t choose that option, but the world that my friends and I used to have just doesn´t appear. In the XBOX is kind different because I can´t open .Minecraft like in a PC