Time Frequency analysis focus on low frequency,high frequency gone

almost all of my frequency analysis result is like shown in the screenshot,mostly focus on low frequency under 10hz,does it mean lack of higher frequency signal?or that's only because I didn't do baseline normalization.after i do a baseline normalization,the result seems normal.I want to ask :is baseline normalization a must-thing to do?if we ignore,the results will be like screeshot shown above,aren't they?

These questions are discussed in the tutorial about time-frequency: