I think grief can definitely cause anxiety or panic attacks. I'm so close with my dad that even just imagining his death has literally caused me to have a panic attack before where I started crying and everything. Grief is a very strong thing and it takes time to be worked through. Grief has many stages and the feeling changes over time. It is very normal to feel anxiety or panic after losing a loved one. It also really shows how much you loved that person or how much they mean to you. Death freaks me out and some days it really gets to me. I was just talking to my friend today about feeling weird all day after I watched a show about the morgue. So just know that what you are feeling right now is very normal, and give yourself the time to ride out the grief and love yourself and take the time to nurture you right now.