I am familiar with this---and, often find it is triggered by a thought/judgemental in my head, sometimes related to a memory, sometimes to anticipated anxiety. Remember it can also go away----try tossing it away---or doing something that really uses all your sense to distract you (for me things like plunging into water, dancing to certain (non-triggering) music, or going to a museum/film/even walking and window watching sometimes helps.
[ even been known, at night, to climb a tree or play in the kids playground---and I am 61yo)