Why does this happen when I see a relative I havent seen in awhile?

When I see a relative I haven't seen in years. Another words, they make no effort to meet up with me or I them and we see each other, they seem like a stranger, as though I have never met them before, my mind just goes blank. For instance today my uncle whom I was close with as a child, but haven't seen in probably 10 years, I will feel weird about him being in my home and just really uncomfortable. Then the person acts toward me like we see each other every week, like nothing has changed and that makes me REALLY uncomfortable on the verge of panic attack and intrusion feeling.