Every year, over half a million people voluntarily jump out of planes just to free fall 13,000 feet to the ground. According to the United States Parachute Association, this daring league of adrenaline junkies, newbies, and skydiving competitors make 3.2 million jumps in a year, and 500,000 of them are first timers.

Whether you’re crossing it off your bucket list or simply addicted to the rush of plummeting down to earth at 120 miles per hour, free falling produces more than just the heart-thumping adrenaline rush it’s known for. Many of sky diving’s effects are physical — though it’s hard to notice them amidst the screams.

Brain

During a traumatic experience, it’s common to feel that time has slowed down or even stood still. Although skydiving might be counted as deliberate exposure to trauma, your brain still processes the stress the same way, causing your perception of time to shift.

In 2007, researchers published an article in the journal Behaviour Research and Therapy on time perception for first-time skydivers and found that people who reported being more frightened also reported the fall lasting longer than it actually was. People who were excited, however, had a “time flies when you’re having fun” experience and thought the dive went by faster than it really did. Objectively speaking, that free fall normally lasts for about a minute.

Ears and Nose

During your descent from a height of 13,000 feet, you’ll also experience rapid changes in atmospheric pressure, which can have a huge impact on your ears and your sinuses. In a review in Current Sports Medicine Reports, researchers investigating the impact of extreme pressure changes inherent in activities like scuba diving and skydiving found that the pressure in the sinus and ears decreases during the flight up, forcing air in through a “reverse sneeze.” But during free fall, pressure increases, squeezing air out of the ear and sinus. These sudden changes in pressure can give you ear and sinus pain as well as vertigo, headache, and nausea.

Internal Organs

From the moment you jump out of the plane to the moment you land, your body experiences a variety of different speeds and accelerations. Javier Avendano, a neuromuscular disease researcher and avid skydiver, tells Inverse that rapid acceleration only “lasts 3-4 seconds — after that, there is high speed but no acceleration, which gives the relative feeling of floating.” This sensation is due to air molecules pushing back against your body as gravity pulls you towards the ground.

After a few seconds of this, you reach a steady speed of 110-120 miles per hour for about 30 to 50 seconds before you deploy your parachute at 3,500 feet and slowly glide down to earth. The speed of the plane you’re riding before your jump is close to the speed when you free fall. “When you come out of a plane, you’re already flying at 100 mph,” said Avendano.

Butt

As of today, Avendano has racked up 1,100 skydiving jumps and hasn’t found any significant changes in his internal organs but has noticed a different biological response before taking the plunge — nervous farts. “With the lower air pressure when you start ascending with the plane [and] tandem passengers scared shitless,” he says, “internal pressure mounts slightly enough for anyone trying to hold in a fart to release it.”