No you don't.
Sitting mindfully is helpful and builds that "mindfulness muscle" but it isn't essential.
Many people don't live in circumstances in which they can sit mindfully for 20 minutes a day. Others would give up on mindfulness if they had to do it because, well, they can usually find something more interesting to do than sitting!
If sitting mindfully isn't your thing, you could aim to cultivate mindfulness in your daily life. How? Try these:
- As often as you remember to do so, take a few calm breaths in awareness. This takes you out of the mind-wandering that so many of us get lost in.
- When you realise you've drifted off into rumination (going over and over negative stuff in your mind) bring your attention back into the present moment and to what's going on around you.
- Walk or stroll mindfully, in other words, bring your awareness to the fact that you are walking, to the sensation of walking, to what you see and hear. You don't need a park or a forest for this (most of us don't have one handy). You can be mindful when walking in your place of work, in your home, or down the street.
Mindfulness as we practise it today was developed in the Buddhist tradition. But historians say most Buddhists have not traditionally practised sitting and meditating, that this was more a practice for senior monks in monasteries - the juniors were busy doing the hard work!
So if sitting in meditation isn't for you, practise mindfulness anyway and you'll still get the benefits of this great life skill.