What Does Internal Bleeding Mean Caused After A Knee Surgery?

Hello my mom had surgery on both knees three days apart and she is currently in a rehab hospital but the doctor called and said that she is not mentally responsive and her blood pressure is very low and she is clammy. What does this mean internal bleeding or what could be the possible cause?

She is 80 years old height is 5'3 had major surgery over 10 years ago where she was bleeding internally and had a portion of her intestines removed.