You might like this:
http://soulanatomy.org/read-this-if-you-feel-like-you-cant-stop-creating-problems-in-your-mind/(The author there is heavily promoting her book under an "org" domain, go figure, so take it with a grain of salt, but the message is still good. I have zero affiliation, the idea just seemed pertinent)
Basically, I don't think there's any sense in trying to shake this feeling because it will always be there. The point of any "retirement", whether it be early or not, is to move from doing what you don't want to be doing to doing what you want. The desire for fulfillment and feeling "productive", will never completely wane, but I think you can learn to focus on less impressive goals. As long as you're always creating "something", or at least get the feeling that you are, you'll be fine. I don't think there's any scale that has to define that "something".
Obviously, as others have mentioned, society has created such highly specialized positions that it's difficult to recognize whether our skills are really bring put to use or not. In reality, there's no way (except qualitatively by an individual) to judge which pursuits are worthwhile and which ones aren't. In the end, there's virtually no difference in being a "number puncher", and being a "visionary" like Bill Gates. The point is that you can get fulfillment and meaning from very small things. In "retirement", your mind may become fulfilled by creating art or volunteering if there are no other pursuits that you'd rather go after.
I think it's a worthless exercise to try to convince anyone that you eventually get over the "having to do something" feeling, because you don't. We have to constantly be doing something - it's in our wiring from evolution. The point is that you can and will learn to redefine what it is you want out of the world and how you're best suited to live it. That's where the importance of having enough money and passive income comes into play in being able to afford that freedom.
But on the flip side, freedom isn't everything. Being overwhelmed with options is not necessarily a good thing, and we have seemingly more options now by FAR than before. (I say seemingly, because the difference in our perceived options are often very little in reality). Sometimes it's better to be "stuck", depending on what you're stuck doing, rather than worrying about what it is that will make you feel alive. Normally, when you're stuck doing something, you'll daydream about what it is that you'd rather be doing, and sometimes those dreams are better left as dreams.
Obviously, I think about this a lot. Essentially, it boils down to the meaning of life in general. If you're not doing what you feel is worthwhile "work", then what's the point? We were born to be producers, not consumers, that's why the idea of retiring (unless you're super old and ready for death) to a beach permanently are not solutions. If you're truly going to "retire", then I think the best way to do it is to travel so that your mind is constantly occupied and you're so busy planning and figuring out logistics that it begins to feel like work.
