Option #1: Oblivion in laudanum.
The solution is extremely Victorian: F.F. Gebrandt's Superior Laudanum, to help you sleep at night. You can find it in the Echo Bazaar (click the "Bazaar" tab), in the shop Nikolas Pawnbrokers. Each bottle costs one Echo, which can be quite pricey if you're trying to sell Whispered Secrets or the like in the Bazaar.
Drinking laudanum is bad for your health, and your Wounds quality will increase a bit one change point), but you can reduce that with F.F. Gebrandt's Tincture of Vigour. I imagine that Gebrandt is an extremely wealthy lady. Alternatively, you can just rest at your Lodgings if your Wounds quality is 3 or higher.
Once you become a Person of Some Importance (PoSI), as with the Tincture of Vigour and Ablution Solution, this option will become less viable; unlike the other two, it will also have a nasty side-affect: every time you drink a bottle of the stuff, you'll become slightly more addicted to it, resulting in the Laudanum becoming less effective.
Option #2: We're all mad here.
Go to A state of some confusion. It will discard and replace all of your Opportunities with new cards, so don't do it if you really like your current Opportunities. Almost all of the Opportunities and actions available in confusion will decrease your Nightmares (though some will abuse your base stats a bit, and one or two will increase your Nightmares while giving you something else you want), and you will leave A state of some confusion once your Nightmares drops to zero.
There are two ways to get to A state of some confusion:
- Go to Mrs. Plenty's Carnival, into the House of Mirrors, and then Gaze Into Dream's Mirror, which requires that you have at least one in Nightmares.
- Let your Nightmares quality increase to 8. You'll be taken there immediately.
A state of some confusion doesn't cost you any Echoes, but has a much worse action-efficiency compared to drinking laudanum. (Laudanum seems to do about 4 change points of Nightmares reduction, and actions in a state of some confusion are more like 1-2 change points of Nightmares reduction.) Not all actions there will decrease your Nightmares, but drinking laudanum will waste some of your time with curing your Wounds, so it's a wash; there's some good reasons to just let yourself go mad. Unfortunately, a few of the actions in confusion have a chance to abuse your four main qualities, and there are a few other small-ish drawbacks, so it's not all upside.
Option #2 if you have Memories of Light: we're all mad here, too.
If you have 10 Memories of Light, then you can spent two of them to go to the Mirror-Marches instead of A state of some confusion at the carnival. If you have at least one Memory of Light, then getting to 8 in Nightmares will take you here instead. The Mirror-Marches are much more generous than A state of some confusion; your main qualities won't be abused nearly as much, and actions that remove two or more points of Nightmares are much more common.
Option #3: Psychotherapy.
In your Lodgings, you'll get an option to Find a way to deal with your Nightmares if your Nightmares quality is 4 or higher. Spend a Sudden Insight (possibly gained via Invite a friend to join you in something terribly intellectual from your Lodgings), and you'll lose 5 change points of Nightmares. Your friend will gain one change point of Nightmares and also spend one action, so you should return the favor sooner or later.
Lacking lesser Rumour items, you can use the Implacable Detective's Business Card to exchange Whispered Secrets for Incendiary Gossip, if you have it.
More Opportunities to acquire Incendiary Gossip can be found by cultivating your connections with Bohemians, the Church and the Great Game.
Note: There is a list of Storylets that result in acquiring Incendiary Gossip, if you wanted to see whether any Opportunities you currently have available would result in Incendiary Gossip (but that would be cheating now wouldn't it ;) ).
Best Answer
No, you may not have multiple Ambitions. The closest you can get is to get to the end of one Ambition, use the Lethean Tea Leaves (which will cost you a bit over $10 USD in Nex), and start another one. Alternatively, you could run multiple characters, each with a different Ambition. (Note that the various Ambitions are not complete, per se: each one simply stops at some point, with promises that the writers of Fallen London will create more content in the future.)
Ambitions are about investment: they're a long-running storylines that give your character a purpose. That being said, they're good fun to follow. Just pick one that appeals to you and see where it takes you.
Edit:
There is now one Ambition that you may pursue in parallel with your main Ambition. It is Ambition: Enigma, and to date, it consists of solving puzzles. (Since the self-annihiliating Seeking Mr. Eaten's Name content has been disabled indefinitely, it is a sort-of replacement for it - without nearly as much pain, agony, tears, and destruction of one's property, sanity, and sense of self.) In fact, its entry-point is a puzzle; the basic clues of which have been collected. Ambition: Enigma involves references to TS Eliot, best known for the Waste Land, JL Borges, whose most famous work is The Aleph, Stamford's The Aleph in the Mirror, and Calvino's Invisible Cities and If On A Winter's Night a Traveller.