Never driven Route 9 myself but this kind of thing happens more than people realise and nobody talks about it because they're worried about looking mental.
What time roughly? And which direction were you heading? Details like that actually matter if you want to cross-reference it with anything.
I've had two experiences near Stonehenge where time just didn't add up. Not driving, just walking. Looked at my watch and 40 minutes had gone somewhere I couldn't account for. No memory of sitting down, no memory of anything really. Just a gap. Felt completely fine physically which is almost more unsettling than if I'd felt rough.
Has anyone else reported anything on Route 9 from around that same night? Worth checking if there were any unusual lights reported in the area. These things rarely happen in isolation and if someone else was on that road that evening I'd genuinely like to hear from them.