Let me just chime in for the sceptics, the stuff is real and if you have a friend or good friends who are involved with legit ruqyah or perubatan Islam circles, ask if you can tag along when they receive emergency distress calls. But beware, because you need to have a certain amount of inner strength and don't go in with this arrogant mentality of thinking you're 'immune' to such things.
What you see will help you decide whether these things are real or otherwise. My best friend went with one of these guys to a patient's house. He was a believer of course but never really thought of it as a big deal. When he got there, there was this young kid. Crawling on the ceiling on all fours, muttering a language he's never heard of. Unless there was a multi million Hollywood CGI set running in the background, I think it's safe to say that it was something supernatural.
Now don't just take my word for it, like I said ask around and accompany these legit ruqyah groups. Just because you've had friends or family misdiagnosed and scammed by dodgy bomohs, doesn't mean you can discredit people who've had experiences with the real deal.
Last but not least, it's in the Quran and hadith, but like other people have explained, it's not right to be fearful of them but know that they exist.