I use my Single Size Brown Biomat and wake up several times each night with some kind of buzz feeling. I used 5-th level as the mat was only slightly warm. Is it correct?

The FIR amethyst mat does not work like a conventional heating pad. 

The mat is only warm to the touch, but it is actually hotter. Most of the energy (in the form of Far Infrared Rays heat) from the mat is transferred by radiation, not by conduction only like by the standard heating pads. Heating pads are hotter to touch but do not produce much-radiated heat. 

The mat should be slightly warm to touch on lower levels, warm on medium levels, and very warm on high levels, but the actual transferred heating energy is much higher.  This warmth is much more penetrative and provides a deep effect. 

Our body temperature sensors do not feel the FIR heat the same as conductive heat when the object is hot. So, the mat should be used at a much lower "sensible" temperature than the standard electric heating devices or pads.

It demands extra care, especially for long or all-night use. If the level is too high, you may feel buzzed or overstimulated.