I am a disabled man with some broken bones that will not heal. I cannot undergo surgery as I nearly died last time from an infection. I am in a lot of pain and sometimes have to take narcotic painkillers to manage my discomfort. Either way, I sleep very poorly due to the pain and/or medication. I have two choices when it comes to Shachris… daven in the zman but be so sleepy I don’t even know or remember what I’m saying or davening well after the zman has passed. I know if one intentionally misses the zman he cannot make it up, so what should I do?
Under the circumstances, this is not considered missing the time of davening “intentionally,” since if you miss the time for davening it is due to your condition and not out of intent.
However, if you miss the time for Keriyas Shema, there will be no way of making this up.
Therefore, you should make sure that you wake up in time for Keriyas Shema, and must recite at least the first verse and preferably the first paragraph.
Beyond this, it is of course best to daven on time, and you should make every effort to do so. But if your davening on time lacks intention and meaning, and this is due to physical circumstances that there is no way of avoiding, then it is permitted (and preferable) to daven later, when you have your full wits and facilities about you.