It seems like slowing everything down would create a calming effect. We look forward to retirement because we won't have the daily stress we have now. The thought of not rushing out the door to get to work and not carrying around the stress of tasks and deadlines brings thoughts of peace and relief.
But when we let go of all of that there's something missing, and that void can create anxiety. The thing that's missing is purpose. Without something to look forward to, without a reason to push forward, it's easy to start feeling lost, and to stop putting energy into life. Slow things down, and enjoy the opportunity, but look for a purpose in the middle of all the slowness. Find something that helps you grow, like learning something new. Set small goals and timelines, and plan rewards for accomplishments along the way. Give yourself new purpose, create something to look forward to, and always include some form of growth in your day. Then the calm is no longer a void, but an opportunity.