One of the tricky questions in singing is the effect of stress and tension performance related (personal stress in general does not affect singing from the first time a singer chooses diaphragm connection as a voluntary choice of action).The inexperienced usually thinks being able to perceive his stress or pressure. This is a superficial way of considering how stress or pressure acts. We can have a perfect feeling of balance and not finding voice, or feeling panicking internally then find a way to relax and idem not find the voice and even find it responding worse then when panicking. Our internal feeling or perception does give a measure of something that is not the measure of our instrumental functioning. Only intrumental functioning will tell you how it is in that moment, and what is with proper energy and the correct level of tension but not too tense or too released and with the good internal time for the first song. Experience and especially the correct structuring of muscles and mental patterns during study and performances will shape in a way to render impossible to be different and not to find them back, but it is not the case while structuring or changing bad habits. So it is important to have a clear way of acting not to fall in the traps of the specificity of this great instrument but not intuitive. First is to stop thinking to control by perception (and stress will put happy an good perceptions out of focus) and start regularly check the connection and do the basic exercises as if it was our first time and with all the cares and not expectations of the first times. Even if we will not find back exactly what we can have we will be in the path for that and not farer. Second yes relaxing a bit but more as a stretching physical way than energetic (music requires its specific rhythm and energy and without we are totally stuck and impotent) and get into the physical internal sensation of songs rhythm and of songs internal consistency (it is at that level that diaphragm connection acts properly). Do not care if you do not feel what you usually feel, just try to find the usual acts and actions, perception will get back and improved after and just after you have lost it.
If we had to put classical voice and pop voice in their extremes regarded differencies in vocal positions, I would say that it is in the way of treating the two positions in which we currently work (in pop for some dark and not high voices or when we want to give more structure to timbre even if losing some extension, we have just one position). In classical we use muscles of appoggio and sustain to obtain two vertical segments of those positions (the blending of registers) while in pop (and often jazz) we use the same muscles to give the illusion of two horizontal planes. Of course this is just the extreme pure, a number nearly infinite of ways of mixing of the two concepts is not only is possible but sign of a good technique and the choice of personal voice over a only academic one.