This condition is commonly called 'tipping' with Bird Of Paradise.
It can be caused by a number of factors including over watering, chemical burn from over fertilizing, root rot, and dry air (lack of humidity).
Using tap water can be an issue with the salts building up in the soil.
Leaving the water to sit for up to 48 hours before using it to water the plant with can help.
Here are some links to refresh you on the care requirements so you can make adjustments to the plant care.