I get that all the time. I need several uninterrupted hours of writing; I can’t just slot in 20 minutes here and there. I need deep concentration.
Mind maps help with that, but honestly the best way to keep it all in my head is to just be in that headspace for hours and hours, thinking and working and writing and exploring. I do my best writing late in the evening, from 10-12, because nobody fuckin bothers me!!