How Do I Know What ‘Normal’ is?

I’ve been sick for so long, I’m not sure I would recognize it if I started feeling better, got healthier.  Is it possible to ‘get better’ and not know it? And still think like you’re not well, like you’re depressed, even though you’re not?  How am I supposed to think, feel, act if I am improving, getting better?  I have been ill for so long, depressed for so long, I don’t even know if I have ever been ‘better’ or ‘healthier’.  If I don’t know what ‘normal’ or ‘healthy’ is, if I’ve never really experienced it, then how do I know when I get there, and how do I know how I’m supposed to be?  I think I’m almost as afraid of ‘getting better’ as I am of staying where I have always been, hurting, suffering,and in so much pain and fear.