Hi. i had trouble sleeping & had twitching in arm & legs & back , only once, prior to going to sleep..is this because of stress ?

Could be, unlikely: If I read this correctly these twitches only occurred once? And not recurring? If so it may be anxiety if you have a history of that condition. It may also be a rare occurrence of myoclonus not tied to any anxiety, medication, or other medical condition - if so this happens occasionally to a majority of people and is not problematic. If frequenting problematic talk to your provider about options.