Well, you are not supposed to lose anything. However, so many people have major problems when moving to Windows 10, that all I am going to say is that if you want to make that move, make sure you have everything you cherish completely backed up somewhere other than on your hard drive. External to your system.
Yes, it can be that bad still. Which is why I am still sitting here running Windows 8.1. And very happy with it. And until Windows 10 has a good chunk of its current issues fixed, it is going to stay that way.