The tricky attacker was booed by his own fans as the Selecao struggled to impress against the 2010 World Cup hosts, and Neymar feels that people are perhaps expecting too much of him.
"I felt sick because of what happened against South Africa. I am not a machine," he was quoted as saying by Globo Esporte.
"I was exhausted after Friday's match, both physically and mentally.
"I just want to keep on playing and help Santos and the national team."
Brazil will be looking to improve on Friday's performance in the upcoming friendly against China on September 11.