Tranny dead..then alive ??

[rattachez]

Had noticed a whirring sound last couple of days.
On the way home Tues. night I started losing power-like
my tranny was slipping. It got worse and then just lost all
gears- like I was in neutral. No more whirring sound- no more tranny.
After a lovley tow home yesterday morning I checked the
tranny fluid and it was very low on the dipstick. I started it up
and put it in gear and it moved forward and reverse in my driveway.
I added some tranny fluid and headed out and it drove fine.
Then after it warmed up I heard the whirring sound again.
It starts when I step on the gas and sometimes lingers for a few
seconds after I take my foot off. So I brought it to the Tanny place too
have them check it out and am waiting too hear. They said if fluid was at least showing on the dipstick it wouldn't completeley shut down like that.
Any guess on the problem?