Lazy version: if you want to feel an emotion, then try to remind it once, then repeat reminding with shorter pauses between emotion. Personally it still makes me laugh (when i remind myself how happiness feels like) with joy within 2-5 seconds no matter how boring or mildly unpleasant other thoughts feel. Heart rhythm speed same as reminding speed works well.
If you don't want to feel emotions or energy then sometimes it helps to imagine zero pressure within your spine (physical relaxation), brainstem (face) and brain (more mental/thoughtless relaxation). Playing with these "pressures" could be used both ways. Increased pressure kinda wakes up (i often try it before getting out of bed in morning) or decreased for relaxation/sleepiness.
For sleeping and calming during day it may be effective to avoid any eye movements for at least few seconds. That reduces desire to keep moving around. Also when desire to move lessens then staying at same position becomes more comfortable. If you keep moving then you also keep feeling like you should move some more because of uncomfortable feelings. That discomfort goes away if movements have been avoided for several seconds.
Stopping eye movements for 5-10 seconds seems to work about as well. This slows down thinking almost anytime.
One way to reduce attention to unwanted thoughts or feelings is to concentrate on them. Avoiding or trying to hate unwanted things rarely works. Very helpful trick has been about 5 second long concentration during which i try to ignore everything else including my sense of location, surrounding and body. If you try to avoid feeling these last 3 things (or at least body) then this tip may work better. Usually after that i feel too tired to think about unwanted thing for some time. It may be useful during dialogues to block out some emotion or thought for few minutes.
If you want to keep certain emotion going for hours or just long time then avoid extreme emotions because you'll get tired fast. Problem is we can't describe emotion intensity objectively and people have to research on themselves what intensity tires them faster and what level lets them care about smaller pleasures.
Also partly why falling in love causes emotional suffering by making other stuff look less significant. Too high hopes from one wanted emotion can make other events often underwhelming.
Moderation can help with partying by not making the rest of your day look boring.
If drug use is common you might notice that when you use alcohol or other sedatives they create certain emotionless emptiness that makes you want to take more drugs or do some extreme stunt to feel more alive. Compounded with lack of memory people may think they have most of the fun when they are confused out of their minds on drugs.
Your desires depend somewhat on how much you think you need something.
If you think it's normal to party every day then getting blocked from
doing it somehow causes grumpiness.
Intense motivation passes faster than weak but more constant willingness to work. Most work need long time and intense desire to start doing important stuff NOW can end quickly, because that's not how you normally feel while doing your job. It's more like semi-bored automated mentality.
One way to get motivation in writing is to shallowly and barely touch the subject. Later it's much easier to write again about this topic.
If you are acting and overdo a emotion then you will not be able to keep it going long without starting to look like a faker. Calm opponent may know that and keep calm while the other side gets tired before minute ends and the emotions lose natural look/sound.