I Feel So Forgotten

DH had ADHD. He is on meds and really trying to work on himself. He works from home which makes it difficult for him to focus sometimes (working from an office is not up for discussion). Sometimes when I need his attention he will say things like "I need 5 minutes to focus on this first." I try to respect that and give him his space to focus on what he was working on before I came in. However, when a half hour goes by and I am still waiting, I get frustrated. If I try to remind him that I am waiting or go back into his office he gets angry and feels pressured. Yet, at least four or five times a week he ends up saying something like "Oh, I forgot you were waiting for me." I love my husband and want him to succeed. I just don't know how to deal with my own feelings of being forgotten about.