Nonverbal is when the cognitive effort required to form words into sentences is too much to bear. Conversation is effortful even for neurotypicals at the best of times. Have you ever had a thrilling 3 hour conversation about philosophy with a friend and felt exhausted afterwards? For autistic people, the baseline effort is higher, and complicating factors are worse . Which topics are a minefield? What are the other person's triggers? What idioms don't mean what they seem to mean? How much introspection do I need to do to answer a simple 'how are you'? Why does everything sound so loud? Do I have to answer questions right now? What's the answer? How do I find out???

When I'm having a meltdown, there is nothing left in the tank that I can remove without compromising my ability to do things like "exist in the presence of light bulbs" or "not be upset by the fact I have hair". I can either go to the effort of finding answers for my girlfriend when I'm exhausted, or I can just barely manage to not want to kill myself to escape the pressures of existence. Because every second of my life, the task of being okay with existing in the real world does take effort. Not much, but sometimes it's the only thing I have energy left to do. Sometimes I don't have the energy to do it.