When we are sick or aren't feeling so great physically, it's certainly ok to take a break from meditation practice. If you do decide to meditate while you're sick, ideally we want to meet our experience with care and bring a relaxed attention to our explorations. Tuning into an overall sense of the body, and the sensations that are happening, can support us in being more intimate with our experience without exerting too much effort.
You may wish to experiment with a body scan practice, especially while lying down. Bringing interest and intention to the experience of bodily sensation can loosen the grip of thoughts that tend to make us feel worse when sick — "I feel horrible," "I wish I were better already," etc.
You could also practice with the focus on external sounds, especially as an alternative to focusing on the breath, as that allows a sense of rest from attending to the body when it becomes too difficult. In the app, search for sound meditations, or try one of the following:
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