The things that have worked best for me over the years sound a little silly perhaps but here goes:
1. singing out loud, often - particularly when upset or down
2. reassuring myself that everything is ok, again better done out loud but possibly not when others are around
3. going for a walk - I tend to walk to a supermarket and stroll through the aisles somewhat aimlessly which is weird when supermarkets can be one of my main areas of stress at other times. It's something I used to do when I wanted to self-harm to get around people and hence away from danger so I guess it just stuck.
4. eating chocolate or drinking a hot chocolate drink, sometimes even holding the warm mug helps
I've done therapy and stuff, but have found the above tends to be more useful for me.
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-M&S
?Two men looked through prison bars; one saw mud and the other stars.? Frederick Langbridge