How long is flexeril (cyclobenzaprine hcl) active. I have been taken 2x10mg pills at night for issues w/ sleep. I get up at 6:30 but around 8 I can no longer stay awake. Wh?

That is too much. You are taking too large of a pdose. The medication is typically written as 5 or 10 mg three times a day as needed to treat muscle spasm. You may want to discuss options with your treating physician.