How do you feel when you've been left on 'read' for a long time and what do you normally do about it?

I don't know. Depends on the kind of conversation.
I am a bit particular about manners and also the kind of priority to give to different topics.
Understanding will stretch so far before I stop taking them seriously.

I'm usually very understanding of such situations as sometimes I'm the person not responding.

They might have a good excuse and I don't need to know it.

Honestly I try to avoid forms of communication that have read receipts.

annoyed when I need an answer. But its always family and I could always call.

Makes me overthink a lot

My dad will leave me on read but we don't have much of a relationship. My social life is non-existent so when I message someone and it gets left on read I just go with the standard well I'm not that important to their life so I'm just gonna go do other things and I will think about it from time to time and upset myself