I saw a chiropractor for neck pain and he did some weird stuff with my neck and i heard a creepy cracking sound. felt like bones were breaking! the chiropractor said that's normal. is that really true?

Adjustments: Most sounds with adjustments are produced from the areas where the bones connect, so just like ones knuckles ,a rapid externally applied force will snap the surfaces together producing a sound and cracking feeling. Pulling apart the two bones creates a cavity which fills with gas and then releases producing a popping noise. Most of the time this is normal as described ,

Manipulation: Of joints especially between vertebral columns which have a lot of carefully constructed spaces to maximize balance and cushion will often result in the escape of gases such as nitrogen, which may contribute to the cracking noise which accompany such movement. An example of this is knuckle cracking.