What should I do about the abundance of waswas (whispers/intrusive thoughts) and distraction during prayer, such as the feeling that someone is watching me?

We advise you to seek refuge in Allah from the accursed Satan and to spit dryly to your left three times when Satan whispers during prayer. Indeed, the Prophet, peace and blessings be upon him, guided Uthman ibn Abi al-As to this when the latter complained to him that Satan had come between him and his prayer and recitation. He said: "That is a devil called Khanzab. If you sense him, seek refuge in Allah from him and spit dryly to your left three times."