transmission woe?

[90LS400Lexus]

The transmission on my mothers 97 Achieva has been working finem but tonight, it did something bizarre. I occasionally drive the car. I was driving it home from a hour drive and when I made a turn in the driveway and started the hill, I pressed the accelerator, but it was like the car was in neutral. I placed the car all other gears - nothing- and when I placed it in "1", after a few seconds, it went into gear and I was able to go on and it worked again in all gears- including overdrive. I parked on the level and checked the fluid and it is full and looks and smells OK. For the past 10000 miles, it will have a slight "shudder" when shifting from 1st to 2nd, but it has not gotten any worse. Is it possible that just the filter is dirty and maybe it picked up some dirt? I made several turns before it did this this evening, but this was the only time it did this. Thanks for any information.

[90LS400Lexus]

Thanks for all of the replies.

Seriously, it must have been a fluke, because the car has been driven 200 miles since- with NO problems. The "check engine" and "ETS OFF" lights are illuminated, so perhaps it is something electronic. I did notice once last evening the speedometer was "fluctuating" a bit, then returned to normal. Perhaps a bad/faulty speed sensor? I guess we will have it and have code ran on the "check engine" lamp. Thanks again.