Because I live in TX my friends love to call my amaryllis "Amarillo" (as in the town), and then they start singing a song about getting to Amarillo by morning!!

Where do you live (what climate) and do you let your bulbs stay inside or outside? At 20 inches, if they are falling over it's likely that they aren't getting enough light. You can try staking them up and then giving them better light, which should make them a little sturdier. If they are beyond hope, then cut them back about half way and see if they will stand up. If the leaves are wimpy and limp (pale and almost see-thru), then you can trim them back to an inch or two and give the plant better light to grow strong leaves.

If the plant is 5 years old...do you let it go dormant each year, or are these the same leaves from 5 years ago?
Hmmm!
Kristi