Salamu alaykum Warahmatullah
Alhamdulilah, the night prayer itself is a ni'mah to perfor. The salaf had many saying bout it and the reasons why one might not be able to get up, here are some,
Al-Hasan al-Basri was once asked: "Why is it that we cannot uphold prayers at night?" He answered: "You are shackled in your own sins".
Al-Fudayl ibn ‘Ayaad said: “If you cannot pray qiyaam al-layl, or fast during the day, know that you are indeed deprived and restricted, chained by your sins.”
A man said to al-Hasan al-Basri: “”O Abu Sa’eed, I sleep in good health, and I love to pray qiyaam al-layl, and I prepare water with which to purify myself, so why can I not get up?” Al-Hasan said: “Your sins are restricting you.” He said, may Allaah have mercy on him, “The slave who commits a sin will be denied the opportunity to pray qiyaam at night and to fast during the day.”
A man said to Ibraaheem ibn Adham, “I cannot pray qiyaam al-layl, so tell me the cure for this.” He said, “Do not commit sin during the day, and He will help you to stand before Him at night, for your standing before Him at night is one of the greatest honours, and the sinner does not deserve that honour.”