you can have dissociation with memory issues and not have alters. i don't know if you have a diagnosis of DID or not when asking this though.

if you don't have DID and dissociated during getting your blood drawn, it is possible that you were feeling on edge/anxious which could have caused a dissociative reaction for whatever reason.

anxiety is one thing that can cause derealization/depersonalization for me but doesn't usually cause an alter to surface unless there was a more specific situation for them to come around or a trigger. there are variations like that too even in some people who have DID. those types of dissociation can also cause memory disruptions. unless you are diagnosed or have other things that concern you to make you think you might have DID, i wouldn't automatically just think it is since there are other things it can be.