And just to confirm,ensure the Jack stands are on a solid surface and able to support the weight while underneath, Solid concrete, not dirt or hot asphalt,do a complete hazard assessment prior to complete a task,ask yourself what could go wrong.
That is so sad and also very disturbing, I never go under my signature unless all the Air is completely drained from the entire system and also put Jack stands underneath where I am just for a piece of mind. Sad just enjoying life.
Prayers are with the Family