Feeling of Sudden Conscious Clarity

It's interesting that you say you have a sudden conscious clarity, but your mind can't stay relaxed mentally. What exactly is it that's going through your mind when you're in this state? Is it all the feelings and sensations? Is it nervousness and anxiety? It never hurts to take a few deep breaths and focus on centering yourself.
As far as the sensations getting too intense, you are correct that the pleasure comes in waves. Imagine being on a beach shore. Those waves just wash over you. The more you resist, the harder they hit you, and the more uncomfortable the experience can be. However, if we relax and bob and sway with the waves, it tends to be much more relaxing and enjoyable.
Find what works for you though. Stay calm, "listen" to your inner body through your feelings and sensations. If something is pleasurable, just try to stay in that moment and live it as long as you can. When it goes away, think about what's coming up next. If everything subsides altogether, just rest in that state as well. It can be a reflective rest on what just occurred or a better spot to "listen" for more body ques that will let you know what to do.
Just stay curious. When your mind "pulls back" follow it and then observe what's going on. There are many variations to each session. You may learn something you never even expected. 🙂