I already hold a BA and MA in arts based subjects. I have now started on an MSc course because I need to take this subject at degree level to be able to teach it in a secondary school (I want to teach this substantially more than the subjects I already hold degrees in).

This year is going to be about trying to get onto a pgce course as well as completing all of the taught modules on my course. I am also concerned about allowing myself time to look after my weight and I know this isn't always compatible with bashing out a dissertation.

On the one hand I would love to be able to do the full MSc because if I pushed for it I'm sure it's not impossible and it would be fantastic to achieve that and inevitably look more impressive to employers but on the other hand I have been advised that a PgDip could be enough for what I am looking to achieve and I have absolutely no desire to have a career in academia and feel that I've already proved myself academically via my other subjects.

I am a mature student whose been away from uni study for four years now and in doing a science subject straight at masters level I dont want to sell myself short by not aiming as high as I can but on the other hand im thinking that maybe not doing the dissertation would make things less hectic in terms of doing the taught modules and having more of a life balance. Hope im not thinking too short term here because I wouldnt want to regret doing the full MSc in the long run.

Thoughts/advice on this would be much appreciated.

I guess it would be a taught MSc, so your research project would only be for 4 months? You may as well do it to get the full MSc I think. It's not that big an undertaking.