Is it bad to fall asleep quickly?

Depends. Short sleep latency as already described may not be bad. Average time to fall asleep is about 11 minutes. Less than 8 minutes may be a sign of a sleep disorder.. It may also indicate sleep deprivation. If there are other symptoms like daytime sleepiness or snoring or visual hallucinations during sleep onset or awakening... Should get it checked.
Unlikely. The term sleep latency is used to describe the time between deciding to try to sleep and entering into sleep. I've read 5-10 min is a desired time. I look on anyone getting there quicker as lucky, great task efficiency. If you are falling asleep during tasks or in inappropriate settings the cocern changes to why & might deserve looking into.