Had flu/cold symptoms yesterday. went to bed and could not stop shaking and was freezing cold, which lasted over an hour. why would this happen?

Chills and fever: Shaking chills usually means high fever, unusual for common cold, but common with influenza. If it doesn't happen again, probably not serious. But it can be a sign of a complication like pneumonia. Take your temperature and contact your doctor, to check for pneumonia or other things that might need antibiotic treatment; or for an oseltamavir (Tamiflu) prescription if it's influenza.