Maybe when you've become accustomed to having to struggle in life, when things seem to change for the better and everything you need seems to be going your way, it's easy to slip into the frame of mind where you worry that all these things are going to get ripped away from you or there's a huge failure waiting around the corner to knock you on your @$$.
I'm slowly realizing that it's important to stay "in the moment" and not waste time or energy worrying about things that haven't happened and may never happen at all. All worrying about the future does is rob you of the ability to enjoy the good things you have in the here and now.
Guilt is another big thing. Feeling that the success isn't deserved or that I didn't work "hard enough" to get all this so "easily". Again, that all goes back to the history of having to struggle through in the past, and being told that if we didn't succeed it was our "fault" for not trying hard enough. Don't feel guilty about your blessings. What you have gained through your past struggles is the knowledge (whether you realize or not) to know what you want and roughly what you need to do to get what you want. Prior struggles teach you and train you what to do and not do in order to get those things. You learn how to sell your skills. You learn how to communicate with potential clients. You have refined your product (you!) and improved your confidence in your skill-set, so you've been able to improve your odds of gaining clients from what you were able to do 2 years ago.
Give yourself a well-deserved pat on the back. Everyone needs to feel that life is finally the way you were meant to enjoy it.