Dern I can soo relate. I was hypomanic for a long time before medication stabalised it. But I stopped it due to many horrible side effects and then I started feeling really dull. Like my life was useless. The music that gave me the great nostalgic feeling was gone. Flat emotion even though I had the interest for the activity I enjoy. My mind was cloudy and similarly could not remember all the things I learnt in collage, difficulty find the right words and was less reactive. Strangely, I blamed it on the medication for making me feel that way(which till now I still have some doubts). However, after starting a new medication that helps mostly with my depression, the dullness and cloudy mind is gone and I feel better than ever. I hope it gets better for you too.