The very first time I accessed my sharingan was during the massacre when I was seven. It was activated due to the high level of emotional distress I was feeling when facing my brother. The moment I realized what happened, my vision became sharper, my senses heightened, and the sheer intensity caused everything to slow a bit. My eyes adjusted to the change almost immediately and I went in for an attack despite my disadvantage.
The world was basically the same in appearance except since it was night, I was capable of seeing better in the dark. As for my body, the chakra needed to sustain the sharingan at my young age was immense and I could feel myself weakening quickly, but I used what little energy I could. Like any technique my kekkei genkai grants, there’s a price.
My mind was in a frenzy at the time. I was confused and scared prematurely to awakening it since I just witnessed my parents being killed before my eyes and undergone Itachi’s Tsukuyomi. Afterwards, I passed out. I forgot the unraveling of my brother’s intentions due to the tears he shed, but that too was probably by design. The memories are blurry at best, but I remember certain aspects vividly.