Harassment At Work - Performance Improvement Plan

My performance in a given company has been good for the first 15 months. There was a supposedly anonymous feedback survey where I gave a negative feedback to my manager. My skip level manager has somehow come to know that I gave a poor review. He confronted me in his room about the negative rating. Ever since that moment, my manager has been very hostile to me. Manager has been writing negative reviews about my performance every month. This happened for 3 months following which I have been put into a performance improvement plan which I have to clear failing which I will be let go. I think they are using performance issues as a pretext whereas they are retaliating against me because I gave a negative rating. Moreover, they are purposely creating a hostile environment by nitpicking faults and passing critical remarks in everything I do, ignoring me in team meetings. I have recently been diagnosed with high BP which I think is because of the harassment. Do I have any legal remedy?