Farah, who timed his run perfectly to win gold in the 5000 metres, said he was feeling more confident than the heat but could still not believe the result.
"It's just unbelievable," he told BBC Sport.
"I had a lot of confidence going into the race. In the heat I didn't feel so good. I knew I just had to hold on and got great support from the crowd.
"Two gold medals - who would have thought that?"
Farah failed to reach the 5000 final in Beijing but used his quick sprint to take glory this time around.