(From a documentary I watched, which originally aired on the BBC). They described cannabis's mechanism of action by saying that the molecules of THC (along with a host of other cannabinoids) binded somewhat perfectly with the cannabinoid receptors within your brain, modulating the flow of neurotransmitters thoughout the brain. By modulating
I mean 'returning to a more normal level'. Primarily either speeding up the transfer of neurotransmitters or slowing them down. Hence the stimulant/depressant paradox of cannabis.
When I'm too hypo (bipolar tendancies) or coming down from stimulants, having rushing/anxious + adrenaline-induced feelings/thoughts, cannabis will calm me down and relieve these symptoms depending on the quality of the weed and how much I smoke of course. But you get the idea.
If I'm groggy, and feeling mindfucked in the morning, usually depressed which seems to effect me most early in the day and then again later in the night. Cannabis uplifts my mood, shifts my perception of everything to a positive one and makes me motivated to get on with my day (slows down my stupid/rushing/mostly negative thoughts, and turns them into positive ones).
Cannabis makes me feel more 'normal'. 6 years of heavy use has no doubt caused that though. But I'm calmer, happier and generally a much more pleasant person to be around. My cannabis use has always been a form of self-medication though really, as I genuinely view it as a medicine.
Cannabis has powerful medicinal properties, if the majority of the dumbass world would just realise that and stop treating it like a worthless plant that just causes a silly high and destroys peoples mental health, I have no doubt the world would be a better place.
To answer the OPs question on how I feel high(stoned) vs sober.
High - Content, at ease, not compulsive (I normally have an addictive personality), increased social anxiety in the wrong setting, happy, thoughtful, analytical, 'centered', able to sleep. The list of positives go on. Don't get me wrong though being stoned does add to social anxiety/awkwardness, only in unfamiliar circumstances though. I don't feel this way around close friends however.
Sober - Depressed, anxious, bored, hyper (lots of excessive hyper-active type thoughts with no direction though so it just feels horrible) OR (no energy whatsoever to the point I won't move from the couch or leave my house for days). I can't focus/concentrate on anything. Acute insomnia often lasting ~40 hours which returns to my normal level insomnia that I've always had (1-3 hours to fall asleep).
I feel use of other harder drugs over the years has also contributed to the decline in my mental health (duuuh). I have a passionately strong view that cannabis should be legal to anyone in the same way alcohol is though.
Edit: I haven't mentioned physical medicinal benfits of cannabis as to not go offtopic, but the relief of nausea and stimulation of appetite/metabolism caused by cannabis is extremely beneficial (especially when you have anxiety and 2 peptic ulcers like me), for people wth digestive and gastrointestinal issues, cannabis will help and virtually cure the related symptoms of them in most cases. This effect of cannabis is its greatest medicinal value imo. For people with cancer, AIDs and other terrible diseases which wreak havoc on the body, cannabis isn't a magic cure, but a very beneficial plant that improves the quality of life and functioning of people like this.
2nd edit: I should add I suffer anxiety/depression and my doctor is begininng to think I have bipolar.