If you are not able to perform Salah while you are standing, you are allowed to perform it while you are sitting. In a Hadith narrated on the authority of
`Imran ibn Al-Husayn (may Allah be pleased with them both) the Prophet (peace be upon him) said to him:
“Offer Salah standing and if you cannot, then sitting; and if you cannot, then lying on your side.”
However, it is obligatory upon you to perform Salah at its due time. Allah (Exalted be He) says:
Verily, As-Salât (the prayer) is enjoined on the believers at fixed hours.
When you go to bed, take the proper means that help you get up for Salah. (Part No. 6; Page No. 362) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.