If at all possible, do not move a lamp that is warm. In addition to the above mentioned issues relating to not shaking a lamp, you have the problem of having to hold on to a hot piece of glass. Worse if you drop the lamp, you get splashed with hot liquid as well as glass. It is best not to move lamps until they are cold to the touch. Do not attempt to fill up or top off your Lava Lite lamp.
Some lamps have a larger bubble of air at the top.
This bubble of air is both normal and is critical to the operation of the lamp. Never operate a lamp with a broken seal or cracked glass. You don't want to deal with the stuff inside your Lava Lite anyway. Most Lava Lite lamps are designed to operate with a 40 Watt appliance bulb. An appliance bulb is the type of bulb that is usually found inside a conventional oven.