I'm so sorry for your loss. I can understand panic and depression from two vantage points-- as someone who lives with them, and as someone who helps others manage them (I work in mental health). I don't know if you have ever tried mindfulness, but this approach has been revolutionary for me. It's especially useful for panic. If you can find a class around you it might be helpful-- I took mine through the psych department of my local clinic. I also second the suggestion to give yourself permission and space to grieve.
In a pinch, I turn to a technique call square/d breathing. Find something square to look at (I carry a piece of paper in my wallet). Use your eyes to track the first side of the square as you breathe in for a count of 4. Then track the second side as hold the breath for a count of 4. Next, track the third side as you exhale for a count of 4. Finally, track the last side of the square as you pause for a count of 4 before starting the process again. It can be calming without the eye movements, simply because you're regulating your breath, but the eye movement is what actually cause neural changes over time. It works in a way similar to eye movement desensitization and reprocessing, which is used for PTSD.
I hope these suggestions are helpful. I will be thinking of you.