I am considering doing a phd. Wanted to ask current Phd students how difficult they find things like being a demonstrator/tutor for undergrad practical classes and tutorials. Also, is it as stressful as people say? because i really like the idea of research into something i enjoy

If you enjoyed your degree course and are still interested in the subject then a PhD is definitely worth considering. It won't be easy but the satisfaction of working at the cutting edge of your field will generally get you through the months when nothing works. As for demonstrating, the classes are usually easy to run and a good source of extra cash. As long as your serious about wanting to do research then a PhD can be an extremely rewarding three years.