Yeah, wait a few days. Do you get night erections? Morning wood? A surefire way to tell is to take a roll of stamps, lick them, roll them once around your flaccid penis and then go to bed. If you wake up in the morning and the stamps are broken, then you've been getting hard in your sleep (as you should be) and your problem is likely psychological. If they're not broken then get your ass to the doctor, particularly if you're overweight and/or have a family history of diabetes.