Around 2/3 of women experience shortness of breath as a part of a normal pregnancy. Neurological conditions such as spinal cord injury, phrenic nerve injuries, Guillain-Barre syndrome, amyotrophic lateral sclerosis, multiple sclerosis and muscular dystrophy can all cause an individual to experience shortness of breath.
On August 2, 1964, the U.S. destroyer Maddox exchanged shots with North Vietnamese torpedo boats in the Gulf of Tonkin. Two days later, the Maddox and another destroyer reported once again coming under fire.
This would suggest there was no second attack, but there was no staging either. Johnson had planned for several months prior to the Gulf of Tonkin incident to ask Congress for powers equivalent to a declaration of war once there was a major incident again.