My mood gets worse/drops whenever my dad is around..What can I do?

Literally, on every occasion, when my dad is in the same room or otherwise, as me, my mood drops, and I feel agitated or aggressive or plain miserable. If my mood actually happens to be normal or up and he is around, it automatically drops or I just feel 'less' as happy as I was. Once when my dad went away for a week for work I felt relieved & calmer :/ :s
I see a counseller because of the long-term illness i have (long story putting it this way) and we have spoken about my relationships with family. I KNOW and realize, despite knowing this to a degree before, why he may be like this (always looking on the negative side, pretty much pessismistic/finds the negative in everything, generally drags me down) & realized how i also at times may act this exact way when I have a sincere amount on my plate, BUT it seems I feel even worse when I am around my dad. I feel better when i am out of the house but i wish i could wonder why... Any advice?