Is it permissible for a traveler who cannot sleep during a long journey to combine prayers by delaying or advancing them due to extreme fatigue upon his return, and are there other cases in which combining prayers is permissible for non-travelers?

If you intend to sleep before the prayer time begins, you must take measures to wake up, such as setting an alarm. If you miss the prayer and wake up after its time has passed, there is no sin upon you, and you must perform it immediately upon waking, as the Prophet, peace and blessings be upon him, said: "There is no negligence in sleep, but negligence is on him who delays the prayer until the time of the next prayer enters."

However, if the time for a prayer that can be combined with the one after it by Jam' Taqdim (combining and praying earlier, like Dhuhr with Asr) has entered, and you strongly believe that the time for the other prayer will expire if you sleep, some scholars have permitted combining them. Nevertheless, it is advisable not to combine them in this case, in agreement with the opinion of the majority of scholars. Yet, you have an excuse if you took measures to wake up but did not, based on the hadith (definition): "Whoever forgets a prayer or sleeps through it, its expiation is to pray it when he remembers it."