Diana Nyad has completed the endurance swim she first attempted in 1978 and attempted three times in 2011. As you can imagine there are issues involved in attempting the swim and they are what stopped her previous attempts.
Jellyfish stings hampered some of her other attempts at completing the 110-mile swim so this time she had a mask fitted that would prevent jellyfish from stinging her in the mouth and face. That would make for a bad day even if you weren't planning on swimming for 53 hours. Despite using the mask for protection against jellyfish stings the mask itself caused problems in her mouth because she had to bite down on it: it created abrasions in her mouth that interacted with the salt water and swelled her mouth and throat. During the swim she stated she was vomiting constantly: for the entire 53-hour trek...I suppose she treaded water while she was getting sick.
She swallowed a lot of seawater during the swim which accounted for her getting sick: she also had to replace all those fluids during the swim. The wind forced the water up high and as you can imagine breathing is a problem in the high waves.
She is 64-years old in 2013: she attempted this swim first in 1978 when she was 29-years old. She looks horrible today from the sun and the saltwater, but she has a two-day freshwater swim scheduled this year. Only 48 hours.