That sounds like you’re overheating to me. Download a program called Open Hardware Monitor (it’s free/open source) and start it up. Then turn on DB and try to play. Then, after you’ve seen the issue, turn DB off. Go back to Open hardware monitor and it should show you how hot your CPU cores currently are and how how they actually got.
Most Intel i7’s idle in between 27-40c depending on the model and, with DB playing, shouldn’t get any hotter than 60-62c but shouldn’t’ start causing any issues until you start getting north of 75c. I have a feeling you’re hitting the 100c limit where the processor starts to clock itself down to keep from burning up based on the issue you said you have.
If you do find out that your processor is overheating you need to re-seat the fan and possibly reapply thermal paste (and you’ll need to remove the other paste first).