2006 Pontiac Vibe unable to accelerato

I was turning right at a stop sign the other day and when I accelerated, nothing happened. The engine wouldn't rev yet it didn't kill and I was able to continue to drive at about 20 mph. I crept along for about 1/4 mile until I found a safe place to pull off. I shut the car off while I pondered who to call. But just in case, I restarted the car and it was like nothing was wrong and I was able to drive away. Today, 4 days later, the exact same thing happened. Again, I restarted the car and I was able to drive like normal.
My check engine light has been on and off for a couple of months but when I had it checked, they told me that the light was off when they checked and that there were no messages in the computer history (or something like that) I have also had recent concerns about my transmission due to hard clunking during shifting. This was going on for about 3 weeks but has disappeared and the car now shifts fine. Could these things be related?