I live in a house built in 1929. Our water pressure has always been very good.

This morning everything was fine, but when I came home from work the water pressure on the top 2 floors was really low. 1st floor is fine. The toilet flushed but when the tank is re-filling it sounds like a slow faucet not the normal surge of water. The sinks and bathtub and shower, both hot and cold are all having the same problem. If not used for a little while, the water starts strong and then fizzles out in 5 or 10 seconds to just a little stream.

I don't know what kind of pipes we have, I don't know enough about it to be able to figure it out. My husband is out of town for a month! But the first floor is fine.

Any ideas?

Since you have some pressure in the first few seconds, and than it disappears to nothing - indicates that there is a restricted water delivery in your plumbing system. Therefore:
1. Since you have a 3 story house, you may have a booster pump that helps with water delivery to the upper floors. If that's the case, check the pump for proper operation. See if elec. Breaker is in ON position.
2. Also, see if shut-off valves for upper floors didn't get accidentally (partially) closed