My father passed away less than a week ago. I’m so sad and lost without him, he was my friend as well as my father. I think I’m coping but then I get very frightened and panic, I just want my father back. It’s really hard and I’m trying to cope. He became very ill quickly and passed away in less than 48 hours. I have lots of lovely memories to look back on but I’m missing him very much.
So sorry for the loss of your dad 
A week is very early days of the grief process. It’s a rollercoaster of emotions, mostly lows unfortunately but we are all here on this forum for you. We all share this awful pain that no one else really understands until they too experience it.
I hope that you can eventually find some peace and comfort in all the wonderful memories you have of your dad 
I’m so very sorry for your loss. You are in a safe space here to express your feelings and sadness. It sounds like you had a lovely relationship with your dad. That in itself is so precious. Panic is a very uncomfortable feeling and there are numerous ways of approaching it. I have found breathing exercises really helpful. Breathing in for a count of four, holding for a count of 7 and breathing out for a count of 8. I normally do about 3 cycles of that when I feel anxious. It helps. I hope it does the same for you. I have also found my GP a great support to discuss the symptoms of grief with. Thinking of you 
I lost my dad over a week ago, have so many fond memories but just feel so sad that he’s not here. It all happened so quickly. I keep expecting to wake up and see him.