Polygraphs don't work, and it was a mistake for you to agree to submit to this invalid test. You'll find polygraph procedure briefly explained on the homepage of this website. A much fuller description is provided in Chapter 3 of The Lie Behind the Lie Detector.

If you work in the United States, then under the Employee Polygraph Protection Act (EPPA), your employer may neither force you to take a lie detector "test" nor take any adverse action against you for refusing to submit to this invalid procedure. In addition, your employer may face heavy fines and civil damages for violation of this law. Judgments in excess of one million dollars for violation of the EPPA are not unheard of.

As for your hypertension, there are no scientific studies of the influence of high blood pressure or any other medical condition on polygraph results. But in any event, polygraph "testing" has not been proven through peer-reviewed research to reliably separate liars from truthtellers at better-than-chance conditions under field conditions in people without a chronic medical.

While polygraph results are generally inadmissible as evidence of guilt in criminal cases, I  think you would still be wise to refuse the polygraph. Polygraphy has an inherent bias against the truthful, and honest people run a high risk of being wrongly branded as liars. On this message borad, you'll find examples of many people who were falsely branded as liars by the polygraph. For a recent example, see, Lie Detector Fraud.

In explaining to your employer your reasons for refusing the polygraph, feel free to mention the information you've learned on this website, and to give your employer my contact information.

In addition, because you are being investigated for what is likely a felony crime, I think it would be wise for you to seek the counsel of a criminal defense lawyer.