Mucus from juicing?? Also tired after drinking.

I started juicing about a week ago. I have been drinking one cup a day on an empty stomach, no fasting though. I juice all organic carrots, beet tops, ginger, lemon, collard greens, and sometimes watercress. First couple of times was great, I felt the surge of energy after drinking it. But about 4th or 5th time, I started to feel mucus forming in my mouth as I was drinking the juice (kind of like my saliva was getting too thick and stringy to swallow). I also felt mucusy that night, but all gone the next day. I didn't juice the day after, until today. This morning I started to drink my juice and immediately felt the same kind of thick saliva/mucus in my mouth again. I also felt extremely tired right after drinking the juice, the energy surge I felt the first couple of times is gone. Now I wonder if this means I am getting allergic to the juice, or that I am cleansing. But if it were the cleansing, would the reaction be so immediate - after a few sips?? That seems more like an allergy. Any thoughts??
I did many cleanses before, not juicing though, and my diet is pretty good (many vegetables etc).
Thanks for any ideas.
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