I took two 5mg pills of flexeril within an hour and a half. is that going to cause any bad effects?

Likely no problem: The 5 mg pill was developed to avoid the side effect of drowsiness with the 10 mg pill. So, you will likely be mildly sedated and drowsy. Don't drive, use power equipment, do any tasks requiring good balance, ingest alcohol, and after about 8 hrs, should return to baseline.

Flexeril: I always treated flexeril as a distant relative of valium type tranquilizers, as sedation is quite a possible side effect of taking the 10.mgs. For this reason you should stay home for the rest of the day and avoid alcohol or further doses of flexeril for at least 8 to 12 hours and only if you really need it for back spasm. Some patients take 10 mgs every 8 hrs. Your pharmacist can also advise yo