Short answers, pulled from the story.
Significant changes in the position and structure of the brain have been found in astronauts who have taken trips in space. These findings came from MRI studies comparing crew members after their missions. Astronauts who took longer space trips were associated with greater brain changes than those on shorter flights.
Redistributing fluids around the body causes balance disorders and distorted vision which leads to a loss of taste and smell for many crew members. Noted changes included a flattening of the eyeball and changes to the retina that can make space travelers' eyesight blurry after too much time in space. This condition contributes to observations of altered speech motor control in astronauts.
In a microgravity environment there is very little mechanical stress which results in a loss of bone tissue approximately 1.5% per month especially from the lower vertebrae hip and femur. There is an increase in osteoclast activity due to microgravity causing the bone to be constantly diminished with no recovery. The rapid change in bone density is dramatic making bones frail and resulting in symptoms that resemble those of osteoporosis.
High levels of radiation damage lymphocytes cells heavily involved in maintaining the immune system and contribute to the lowered immunity experienced by astronauts. Galactic cosmic rays present further challenges to human spaceflight as the health threat from cosmic rays significantly increases the chances of cancer over a decade or more of exposure. Solar flare events though rare can give a fatal radiation dose in minutes.
The only humans known to have died of exposure to vacuum in space are the three crew-members of the Soyuz 11 spacecraft who perished during preparations for re-entry from orbit on the 30th of June 1971. Jim LeBlanc remained conscious for about 14 seconds before losing consciousness due to hypoxia when his suit pressure dropped in less than 10 seconds. As he stumbled backwards he could feel the saliva on his tongue starting to bubble just before he went unconscious.