1) Thank them for thinking of you and tell them you'll think it over 2) Ask youself, "Am I able to? Do I want to?" Saying yes out of obligation makes it feel like a chore 3) Keep your "no" short and sweet with no explanation or apology. You don't need to explain why you said no.
Yin Yoga- Use a timer (I use the Insight Timer app) and hold each pose for 3 minutes
Danging Squat Dangling Squat Caterpiller Savasana (Do this one for 5 minutes)