Yes. Usually I can attribute it to sleep or hydration or exercise etc, but since you've ruled them out, sometimes I've found it can be due to an unmet emotional need, often loneliness or anxiety (currently dealing with this). It's like the brain just refuses to stick on the thing I want it to. Took me a long time understand this, as emotional awareness isn't the easiest thing for me. Meditation has helped to get in touch with what's going on.