The disconnection one feels from being in a state of lacking (typically physical needs that throw off homeostasis) in times when needed to perform.
Hunger, fatigue, dehydration and other symptoms in the body can lead to feeling like a basking lizard on a rock.
Signs of Lizard Brain include but are not limited to: disconnected speech, idle thinking and stillness, stumbling on words, intense desire to hunt for food or water, prolonged closing of one's eyes yet staying awake, and being drawn to warmth. Signs typically improve after acquiring one's needs and the ability to focus on the task at hand returns.
"Dude, I drank way too much last night and I am really out of it today."
"Go get some water to shake off that lizard brain. You are obviously thirsty and we need to get this project submitted."
*one trip to the water fountain later*
"Alright, thanks. I needed that. What's next?"