When you stay in a hot tub for too long then your core body temperature can increase above normal which can lead to health issues and thing such as dizziness, nausea and possible loss of conscience.
If you're in a hot tub and start getting dizzy or nauseous then you should get out of the hot tub because it means your core body temperature is rising too much and if you don't get out of the hot tub you could become unconscious and then possibly die.
When using a hot tub you should get out of the hot tub every 15 to 30 minutes to avoid any health issues and do not stay in the hot tub longer than 30 minutes because you could harm your health if you do.
I stay in my hot tub for 15 minutes then get out and take a break from it for awhile and then come back and sit in it another 15 minutes.
Staying in a hot tub longer than 30 minutes at a time can cause extended fever which can result in organ and tissue damage, heart attack, stroke and even death.