missing objects

Hi! I know this will probably sound like a newbie or sth but I’m really in need of somebody telling me what has happened to the gameobjects I’ve had!
The last time I closed unity and saved my project I had some objects in the scene, but now that I opened it I noticed some of my game objects are missing from the scene and they have turned red in the Hierarchy panel. What can I do to bring them back?

For anyone coming to this question thinking that all of their scene objects are missing when reopening a recent project don’t forget to double click on your scene to open up the objects you had from that scene in your hierarchy. Its just one of those little things to remember

game objects don’t just delete themselves. you probably had the scene running when you added a bunch of stuff- came back later and it was ‘gone’. Any changes you make while the scene is running are reverted when you stop the scene.

It’s not the case that I added all the stuff last night. In fact I had added some of the objects missing now, earlier and I had no problem with seeing or working with them every time I opened unity. And as I mentioned I don’t think the objects are deleted, 'cause they do exist in the Hierarchy panel and when clicked on them, their gizmos can be seen. I think they’re kinda disabled.