I'm Catholic but am researching Islamic faith and found that you are buried lying on your right side facing Makkah. They second part was explained, but I couldn't find a reason for the first part. Any explanation is appreciated, thanks :)
It is preferred to bury the deceased on their right side, but it is also permissible to bury them on their left side. Facing the qiblah (direction of Mecca) is considered mandatory by the majority of scholars, while some scholars consider it preferred. Since one has to be buried facing the qiblah, one has to be lying on either right or left side. The right side is preferable based on the sunnah (tradition) of the Prophet ﷺ while sleeping and while praying (when one is unable to pray standing up or sitting down).
يجب وضع الميت في القبر مستقبل القبلة، هذا هو المذهب، وبه قطع الجمهور، وقد ذكره المصنف بعد هذا في الفصل الأخير في مسألة من دفن بغير غسل أو إلى غير القبلة نبش، وقال القاضي أبو الطيب في كتابه المجرد : استقبال القبلة به مستحب ليس بواجب والصحيح الأول، واتفقوا على أنه يستحب أن يضجع على جنبه الأيمن، فلو أضجع على جنبه الأيسر مستقبل القبلة جاز، وكان خلاف الأفضل لما سبق في المصلي مضطجعا، والله أعلم
— NOTE: My own translation, so treat with care:
The deceased should be placed in the grave facing the qiblah. This is the major view and what the majority of scholars stipulated. It is mentioned in the last chapter in al-Musannaf under "Who is buried without washing or not facing the qiblah, their grave may be dug." Al-Qadi Abu al-Tayyib said in his book Al-Mujarrad: Facing the qiblah with him [the deceased] is preferred but not mandated. It is preferred to have him lie on his right side. If he is made to lie on his left side, it is also permissible but it is not what is preferred based on what was mentioned earlier in about praying while lying down, and Allah knows best.
The preference of burying people lying on their right side comes from a hadith that is ruled as hassan (good, in terms of its authenticity grade):
أن رجلا: قال يا رسول الله ما الكبائر؟ قال: هن تسع ـ الإشراك بالله، وقتل نفس المؤمن بغير حق، وفرار يوم الزحف، وأكل مال اليتيم، وأكل الربا، وقذف المحصنة، وعقوق الوالدين المسلمين، وعمل السحر، واستحلال البيت الحرام قبلتكم أحياء وأمواتا
'Umair, A Companion of the Prophet (ﷺ) said: A man asked him (the Prophet): Messenger of Allah, what are the grave sins? He replied: They are nine. He then mentioned the tradition to the same effect. This version adds: "And disobedience to the Muslim parents, and to violate the sacred House, your qiblah (direction of prayer), in your life and after death.