What is the ruling on practicing masturbation by lying on the stomach and using a pillow, while feeling remorse and seeking forgiveness after finishing, and does that affect sleep comfort?

This act is forbidden masturbation. You must hasten to repent and not return to it. Occupy yourself with beneficial words and deeds, and do not succumb to evil thoughts. Whenever a sin occurs, repentance is obligatory. To treat insomnia and the feeling of discomfort during sleep, it is recommended to remember Allah before sleeping, recite the prescribed supplications, and supplicate to Allah to remove the insomnia.