It is always good to be open and honest with your medical team.
As you said, it can skew the test results, and you don't want them to assume something that isn't happening. Likewise, when they are looking at possible treatment options, they will try to find something that works with what you are doing and not something that is contraindicated.
They have probably seen it all, so there is no reason not to tell them. Medical records are private, so no one else needs to know until you are ready.
Hopefully, the scan shows it was something simple like standing for too long and not anything more serious.
Thoughts and prayers are with you.