There can be danger associated with turbulence; however, what you experienced was not at all dangerous (with one exception), just uncomfortable, especially to those who lack understanding of aerodynamics and the physics of flight. The one exception is that there can be some danger to passengers unwise enough to loosen or unfasten their seat belts during flight, as severe turbulence can result in them being "thrown" from their seats and colliding with hard portions of the aircraft structure and/or other passengers, resulting in injuries. I have never understood why passengers almost automatically take off their seat belts when the "seat belt light" goes off (or why the airlines insist on turning that light out after takeoff). Basically, airplanes fly by maintaining a low pressure area over the wing, resulting from the shape of the wing and its movement through the air. Lift varies with angle of attack, meaning the angle of the wing to the air it is moving through. Since air is constantly in motion, the angle of attack (chord line of wing - leading edge to trailing edge) relative to the wind direction (motion of the airplane combined with the direction and speed of the wind, which varies), can result in varying lift forces as the airplane maintains a constant (or near-constant) attitude relative to the ground. Most of these changes in air currents are relatively small, and are not felt in the airplane; however, in areas of stronger changes in air currents (especially over the desert in summer, with alternate columns of rising and descending air, many of which are rather strong), the effective angle of attack of the wing changes frequently and, sometimes, strongly, resulting in rapid changes in the lift vector, resulting in sharp, frequent, but usually short, ascents and descents, i.e.: turbulence. Aircraft are designed to structurally withstand nearly all turbulence, to an extent that you would not believe. The only truly dangerous turbulence is found in and around thunderstorms, which contain up and downdrafts of incredible force, with severe shear between them. Although it is possible to fly through a thunderstorm without losing control of the aircraft (the primary danger there), it is difficult, and structural damage can result from the extreme forces encountered in them. Microbursts, which have caused some crashes on approach and at low-level, are an outflow of the downdrafts from thunderstorms. That is why pilots generally avoid thunderstorms, in addition to the potential for encountering hail or ice in and around them.
Clear Air Turbulence (CAT) is not, technically, a low-level phenomenon. By definition, CAT results from shear between relatively calm air below the jet stream and the much higher speed airflow in the jetstream, which can be extremely intense if the transition between relatively low-speed (and, often, different direction) airflow and the extremely high wind speeds of the jet stream is relatively narrow (say, a few thousand feet). In such instances, the shear and turbulence encountered there (only at hign altitudes) can be severe, possibly leading to a loss of control. That is not to say that turbulence does not occur in clear air at low levels, it does, but it is not termed CAT. Turbulence is not only associated with clouds, but usually results from interaction of wind and terrain, along with heating of the earth. Wind across hills and mountains typically results in waves of turbulence (think of water in a stream flowing over rocks, it is a similar effect) which can extend to quite high altitudes (strong winds over mountains can result in "mountain waves" which have a wave pattern that can extend downwind from the mountains several hundred miles, with both smooth air in the waves and very turbulent air in rotors beneath the crests and above the troughs of the waves). Differential heating of the earth's surface results in rising columns of heated air, which spill over and become nearby descendin columns of air as they cool, often reaching altitudes over 20,000 feet, especially in the deserts. All these factors combine to result in constantly changing wind speed, direction and orientation throughout the air mass.
In summary, I know you had an unpleasant ride, but you really were in no danger. I strongly recommend that you always keep your seat belt fastened when a passenger on an airplane (pilots never take off or loosen their seat belt from before engine start until after shutting down the engines at the destination - there is a good reason for that). Next time you fly and feel some bumps, just remember that the airplane is reminding you that you're flying, not just riding a bus.