My lucky bamboo has been doing great then, without any warning, it just seems to be sick. What should I do?

Keep your lucky bamboo warm, 65-85 degrees and exchange the water out once a month until it perks up.  Then change the water out every 3 to 4 months.  Use room temperature bottled or spring water.  As long as the stem does not turn yellow and mushy, your lucky bamboo is fine.  The yellow tips could have developed due to the use of tap water, lack of water, low temperatures or too much sun exposure.  Keep the water level just above the root line at all times.  Using a quart bottle, add 6-8 drops of the Green Green fertilizer (or another brand of water-based fertilizer) and then use the water from the quart bottle each time you add water to your plant.