Upper UTIs are infections of the kidneys. These are potentially life threatening, if bacteria move from the infected kidney into the blood. This condition is called sepsis. Sepsis can cause dangerously low blood pressures, shock, and death.
So whe you hold your breath, you stop getting oxygen in your lungs that go to your heart. The oxygen level in the blood drops, so your muscles need more oxygen, so the heart pumps faster. This is like running, your muscles need more oxygen so heart pumps faster
2) When you are holding your breath you can feel that you need to breathe. The sensation you are feeling is not the lack of oxygen, it's the build up of CO2. By holding your breath you are keeping the CO2 in your blood stream and lungs-this makes you feel desperate for air.