1 thing that can happen to your body in space is your body gets weaker. This happens because the body has different responses to the weights it lifts under Earth's gravity
Many parts of the cardiovascular system, including the heart, are influenced by gravity. The veins in our legs work against gravity to get blood back to the heart. Also, the size and shape of the heart, for example, changes with microgravity and the right and left ventricles decrease in mass.
With the reduced blood flow to the muscles, combined with the loss of muscle mass impacts aerobic capacity. After 9 - 14 days of spaceflight research shows that aerobic capacity is reduced by 20 to 25 percent .
You also lose bone while in space. In the text, it says "On Earth, the effects of gravity and pressure are needed to maintain our bones.". Research also shows that a 3.5 percent loss of bone occurs after 16 to 28 weeks of spaceflight. About 97 percent of this loss happens in weight-bearing bones, such as the pelvis and legs.
Finally, Your Immune system suffers. This probably happens because of radiation, microgravity, stress, isolation or changes in the circadian rhythm – our 24- hour cycle of sleep and wakefulness on Earth.