OD...as in over dose of drugs,or OD as in feeling strange or different (odd).
They mean they do not feel like themselves - something not right.
Od can mean a few things eg one can feel odd in I just dont feel the same like I might be coming down with something like a cold eg or OD can mean overdose in drugs or drink eg another is feeling odd one out does not fit in with family and friends
Judging from the way you write, you ought to feel a little "od."
Unwell? feeling sick ?
probably odd like cousin it!
could mean their oeverly distracted!
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