because, again, this is a serious issue (at least on my part), I'm fed up with the standard sleep-at-night day-to-day routine.
if you want to sleep in the day, then by natural extension this means you would be awake at night. You have tried sleeping in the day, but from your story, it sounds like you had already been asleep the preceding night. which would naturally make it senselessly impossible to sleep during the following day. However, if you had been awake for the duration of the previous night, it seems it would be quite easy to sleep during the day. Have you considered trying that