In any situation the best option to quit the job is to 'quit on a good note'. However, in case of adverse conditions, you may send your resignation letter either by email or registered post (Ensure you obtain acknowledgement) with the options either serve the notice period or to pay the notice pay. If you go on medical leave and join other organization without reliving by your current employer, may be treated as breach of contract as defined under Indian Contract Act, 1962 and thus your employer may take you to court for compensation. The best way is to send the resignation by registered AD post wherein you can clearly mention whether you would serve the notice period or pay the notice pay.