Related by context. Frequent words. (Click for all words.) 54 sleepiness 54 attentiveness 52 drowsiness 52 vigilance 51 reflexes 48 calmness 48 cognitive abilities 46 arousal 46 tiredness 46 cognitive function 46 cognitive 45 cognition 45 irritability 44 sleep deprived 43 restlessness 43 exertion 43 alert 42 drowsy 42 caffeine 42 stamina 42 sleep 41 concentration 41 endorphins 41 disorientation 41 melatonin 41 decisiveness 40 co ordination 40 coordination 40 comprehension 40 cortisol 40 dopamine 40 intensity 40 blood sugar 40 awake 40 metabolism 40 blood glucose levels 40 serotonin 39 endurance 39 hyperactivity 39 dexterity 39 preparedness 39 posture 39 aggressiveness 39 responsiveness 39 agility 38 physiological 38 mindfulness 38 willpower 38 sleeplessness 38 forgetfulness 38 abilities 37 sharpness 37 gait 37 mental 37 reading comprehension 37 reflex 37 assertiveness 37 Caffeine 37 fatigue 37 intoxication 36 moods 36 fluency 36 metabolic 36 lethargy 36 situational awareness 36 hyperactive 36 consciousness 36 morale 36 awareness 36 bone density 36 sleep deprivation 36 stressful situations 36 neurotransmitters 36 aptitude 36 habitual 36 problem solving 35 hallucinations 35 senses 35 hypoglycemia 35 facial expression 35 potency 35 sleep disorders 35 professionalism 35 slurred speech 35 instinctive 35 facial expressions 35 acuity 34 composure 34 libido 34 teamwork 34 superhuman 34 aggression 34 peripheral vision 34 dozing 34 caloric intake 34 fasting 34 behaviors 34 competence 34 stimulants 34 anxiety 34 momentary