Should the first word after a dash used as self-interruption be capitalized?

When writing dialogue, a dash can be used to denote interruption. For example:

“Hello, can I ask you about—”

“No.”

If a character is interrupting themself, should the first word of the interruption be capitalized? In other words, should the word oh be capitalized in the following quote?

“Have you seen — oh my God, you’re him!”