"Beat a path to thy neighbor's door" still applies to us. I've explained it to people that I go in and out of feeling social, I expand and contract basically in cycles. When I'm not responsive to "you" I'm not being responsive to anyone else either, my world has shrunk and I go introverted again for a time. It has nothing to do with how I feel about you, I just get like that and I always have.

This has worked really well for me, with the people who are willing to get it. Often they tell me it's the same for them.

I can't stress this part enough: People are making up reasons for why you aren't responsive in the absence of you telling them why. The imagined situation, due to all of our little self esteem and confidence issues, is that it's about how you feel about them in particular. I'd tried to explain this to my mom so many times over the years and what eventually did it was me explaining that I go "invisible" on Steam and Battle.net for instance when I'm like that. I even hide from the people I just play video games with. She recalled her sister being a bit of a recluse and got it finally. Your examples might be different, but you do owe your friends that explanation of what it's like to be you, so that they don't think this is what it's like to be them.