وعليكم السلام ورحمة الله وبركاته The Khushoo is not a condition for the validity and correctness of the prayer but it is obligatory on the one who prays to the best of his ability. So if you feel that Khushoo in your prayer was less because of some reason then it does not nullify the prayer. However it does reduce your reward as mentioned in the Hadith of Ibn Abbas may Allah عز وجل be pleased with him ليس لك من صلاتك إلا ما عقلت منها and the meaning of the Hadith is that a person does not get any reward from his prayer except according to the amount of Khushoo he had in it. Also in another Hadith narrated by Ammar may Allah عز وجل be pleased with him that the Prophet صلى الله عليه وسلم said a person may pray but he only gets a tenth from its reward, or a ninth of it or its seventh etc. And Allah عز وجل knows best.