My cat didn't recognize me and got aggressive after seeing another cat.

[MissFoxy]

Hello!
This morning I went to walk with my boyfriend's female cat. Usually he doesn't go to walk with his cat that often(once/twice a month), so I decided it would be ideal to walk with Molly(cat's name) around 30minutes.
Everything was perfect until she saw another cat for the first time in her life.
The other cat tried to reach her, and Molly started hissing, so I decided it would be enough and tried to pick up Molly, but when I was trying to pick her up, she started screaming(I never heard her meowing like she was in terror) and attacking like I was trying to kill her. She was able to get both of my hands bleeding and I lost the grab, so she ran away.
It took me around 5-10 minutes to finally find her again. And fortunately I did find her and grabbed the strap so she wouldn't run away. She still growled and hissed at me like she was in terror and didn't let me touch her. I waited for her to calm down and tried to play with her using my hairband(she loves to play with those) and it took around 5 minutes until she recognized me and let pick her up.
I took her home and she was purring and asking for petting like nothing happened.

She has never feared me and growled at me.
What happened her to act this way?
Should I be concerned about this behavior?

 

[dkb817]

I wouldn't be concerned at all as the sudden aggression has a clear cause - seeing the other cat. She lashed out at you, not because she temporarily forgot who you were, but because she was freaked out by the other cat and was in fight-or-flight mode. Now, if she continues acting like she doesn't know who you are, THAT would be something to worry about.

I would say, however, that if she acts like this when seeing other cats, it'd probably be best that she no longer go for walks outside because next time, she could either wind up hurt, hurting you, hurting the other cat, or worse.

 

[ArtNJ]

A completely normal thing. Most cats cannot be picked up when seriously stressed or you risk an attack. Agree that walks are a bad idea for this cat. Since the cat is leashed trained, you might be able to take the cat in the backyard safely to play. Although even there, you never know what might scare the cat.