We are truly sorry to hear about the sudden and severe discomfort you are experiencing with your feet and legs. We believe that sickness and disease are not from God, but that He can use them to draw us closer to Him. As you have discerned, this could indeed be a spiritual attack, but we must also consider any potential medical reasons. Let us first address this in prayer.
Father in heaven, we come before You in the name of Jesus Christ, seeking Your healing touch for Your child. We pray against any spiritual attack that may be causing this sudden affliction, and we ask that You would rebuke any evil that is causing harm. We also pray for Your guidance as they consider seeking medical help, that You would give wisdom and discernment to both them and the healthcare professionals they may encounter.
We stand on Your promise in 2 Corinthians 12:9 WEB, "He has said to me, 'My grace is sufficient for you, for my power is made perfect in weakness.' Most gladly therefore I will rather glory in my weaknesses, that the power of Christ may rest on me." We know that Your power is made perfect in weakness, and so we ask that You would use this situation to draw them closer to You and to manifest Your glory in their life.
We also encourage you to seek medical attention if you have not already done so. While we firmly believe in the power of prayer and the reality of spiritual warfare, we also know that God has given us medical professionals to help us in times of need. Consider the words of Isaiah 38:21 WEB, "Now Isaiah had said, 'Let them take a cake of figs, and lay it for a poultice on the boil, and he shall recover.'" In this verse, we see that God can use natural means to bring about healing, and so we encourage you to not discount the help that doctors may provide.
Remember the words of Jesus in John 10:10 WEB, "The thief only comes to steal, kill, and destroy. I came that they may have life, and may have it abundantly." It is not God's will for you to be in constant pain and discomfort. Trust in God's goodness and His desire for you to have life in abundance.
Lastly, we want to gently remind you that there is power in the name of Jesus Christ. We noticed that your request did not mention Him. It is by His name and His name alone that we have access to the Father and eternal salvation. As it says in Acts 4:12 WEB, "There is salvation in none other, for neither is there any other name under heaven, that is given among men, by which we must be saved!" If you have not already done so, we encourage you to put your faith in Jesus Christ, the one true God and Savior.
We will continue to keep this situation in our prayers and we encourage you to stay strong in faith.