I'm 75 and just spent 4 days in hosp w/ pnemonia. Iv's etc and 4 days of anti bi at home. No lung prob. Now but also no energy. Is this normal?

Yes. As we get older, it takes longer to bounce back. Let your body guide you to what you need and for now rest!
Common. They hospitalize you when you need treatments like IV fluids & high dose antibiotics to turn the tide of the illness. How long you are in and how long it takes you to recover varies with many factors including type of pneumonia, complications, pre-hospital health, age, etc. I had a 3 yo that spent 4 weeks in an ICU and 2 more on the regular floor before going home to convalesce. You are blessed.