We only have a few basic needs as humans, but they are VITAL and when they're absent, it triggers survival mode for us, better known as flight, fight or freeze, wherein your sympathetic nervous system kicks in and prepares you for survival. Your digestion stops, your libido drops, your platelets thicken just in case you need to clot your blood quickly (yes, your body is this smart). Your heart rate quickens, blood pressure shoots up and specific hormones are secreted like cortisol and adrenaline.