I know it's wrong to lie, but I really need a break?

I don't think it's that bad. We all need boundaries, even with our family, but I would try next time to be a bit more upfront, you don't need to lie to get out of things. If you had boundaries to begin with you wouldn't feel that you needed mother's day away from them as you would have already been having time for yourself and mother's day wouldn't have seemed so overwhelming. Remember the boundaries must be set by you.