You drop your substance. Some time later, you feel slightly 'off.' Lots of people experience this as nausea, but you don't necessarily have to. You'll probably feel scared and tense. Just talk these feelings away. They're just being caused by you, not the trip yet.
So the 'off' feeling culminates into a full fledged "headspace." Depending on you and your drug, you might start seeing visuals, you may not. Usually you'll get engaged with a thought, event, or concept that's important to you. Go forward positively and you'll usually end up feeling good and feeling that you're gaining important new perspectives and wisdom on the subject. If you go forward negatively, then these thoughts will just swim and cycle over a lot and be really aggravating.
If you dosed a lot, then the experience kicks up, and you get even less control over your thoughts. But you can still control your "mood" relatively, and if you keep it positive, it should still be good. The thoughts on a heavy dose are less verbal, and less concrete and very abstract. Just feel good about understanding what you understand, and try to understand what you don't, but don't feel frustrated or negative over elements you can't grasp (yet).
On the comedown, write down all the thoughts you can remember, or talk to someone about it, or make a drawing or painting, or if you're feeling tired, just some music and relaxation. Whatever works best for you to process a heavy event. You will likely feel either empowered and happy, or at least relieved and released. Sometimes you could feel bad. I haven't experienced that ending yet though.
And no matter what happens, if you lose your grip, just repeat over and over "I took a drug. It'll be over soon. I took a drug. It'll be over soon." That life-raft mantra has gotten me through everything so far.
Being happy isn't a necessity for tripping. If you feel suicidal sometimes, then it might be better to give it a miss.
One can always fnd comfort knowng their Mr., or Miss(Swilow in this case)- is simply n existnce 
