I have a living room ceiling to sheetrock and one joist is lower by at lest an i

I'm taking it that this is a bow in the joist?. if the joist is bigger than a 2x4 and is not supporting an upper floor or heavy weight in the attic, you could snap a chalk line across the length and cut off the offending protrusion. if it is a 2x4 I have had some luck using another 2x4 with an opposite bow and airnailing on one end and working my way to the other end by flushing and nailing the boards together. the opposing bow counteracts the original to create a straighter board. two ppl are sometimes required.