Not Accelerating properly?

Transmission problem
2001 Infiniti I30 6 cyl Automatic 175, 00 miles

Yesterday, after driving about 20 miles at 60-70 mph I stopped. When I started the car again and began to accelerate, it would not go above 20 mph. It acted as if it were in low gear (which it was not). I drove slowly. Around, making a few stops and turns and it self corrected. After stopping for about 30 minutes, I returned home and did not have the problem on the return trip.