Is having a heart rate of 142 bad?

Yes it is.. and quite serious also. Is that your resting heart rate? I went to the doc yesterday for a check up.. My resting heart rate was 144 (i"m 21).. the doc said I have extreme tachycardia. I have to go back today for a next set of test to be done.. U should see a doc asap if that's your resting heart rate. Also if you're experiencing dizziness, back pains and chest pains.