Big deep vertical line caused by Botox for horizontal line in forehead. (Photo)

When the forehead muscle is injected there can be a recruitment of fascicles that are still working to cause this line and it can be treated with Botox to each side or with filler but it will eventually go away on its own

I do not know who told you the line comes from sleeping on your side but they were right. There is no muscle that can be accountable for this line nor the Botox itself. Buy a flat pillow and learn yourself to sleep on your back! Cheep and effective.