A normal way to react to a death?

My child's grandfather ped away in a very unexpected situation. We are very much in shock... he was only 49. I have bad anxiety, and though I am on medication for it... it still gets pretty bad in times of stress. Since the death I have had a very depressed, but eerie feeling... as if something else bad is going to happen. Like that "impending sense of doom" feeling. It feels lie a 100lb weight sitting on my chest and a burning sensation. Also, in funerals in the past, I feel this unwanted urge to escape the situation. My heart starts racing and I have a panic attack. I loved this man and his family VERY much so not going isnt an option so please dont suggest it. I will probably sit with my family towards the back just in case, but I dont even want to consider having to get up as I feel it is disrespectful and I dont want to offend anybody. HELP!!! : (