NO NO NO NO! Don't take that stuff.
Greater celandine is not 'slightly' toxic, that stuff is irritant, and outright fucking poisonous! The sap is physically corrosive and has on occasion, been used as a wart treatment, to burn them off, as it contains a cytotoxic compound.
There is a mixture of isoquinoline alkaloids in the plants upper parts, I believe they may be different from those in the root but I am not sure enough to say confidently it is indeed so.
Amongst those in the above-ground parts and the sap include sanguinarine, which is particularly nasty, although there is very little in there, and to cause acute toxicity one would have to take several tens of grams, this alkaloid has caused some outbreaks of serious poisoning in some countries, where greedy fucking bastards either bulked up edible cooking oils with the cheaper seed oil of the prickly poppy (Argemone mexicana), or apparently via large-scale skin contact also.
It isn't acute toxicity I am concerned about in this particular case, with Chelidonium, but chronic toxicity, the oil of prickly poppy seed, when fed to rats, caused degeneration of the heart muscle tissue, and it also causes thickening of lung tissue, specifically of the alveoli, the small structures with very fine walls that are located deep within the lung, and are the part responsible for the diffusion of oxygen from the lung to enter the blood.
Also hepatotoxic, and I believe, toxic to the kidneys. Sanguinarine (and dihydrosanguinarine, which is definately present in Argemone oil, but I am not sure if its present in celandine) are potent pro-oxidants, producing a crapton of reactive free radicals which go on to bugger up cells left right and center. Severe acute poisoning by argemone oil (due to sanguinarine and dihydrosanguinarine) results in the abovementioned degenerative and cytotoxic effects, and causes a condition known as epidemic dropsy (dropsy is an antiquated term for oedema, fluid retention within tissue)
Sanguinarine is also an uncoupler of oxidative phosphorylation, oxidative phosphorylation is the means of burning fuel (in the biological sense) and turning it to energy, uncoupling oxidative phosphorylation prevents utilization of that energy, in effect forcing the mitochondria within one's cells to burn up more ATP, without providing any actual power from doing so, resulting in dissipation as mere useless heat, making this compound a nasty mitochondrial toxin. The banned-and for a bloody good reason weight loss supplement dinitrophenol acts this way, potently so, and causes massive overheating of the body, and a great reduction in the ability to utilize fuel and produce energy, use of DNP by bodybuilders and people wanting rapid weight loss has produced quite a lot of fatalities.
The main isoquinoline alkaloid present within Celandine, is coptisine, which is a reversible inhibitor MAOI-a, just like harmaline, harmine, tetrahydroharmine, the monoamine oxidase inhibiting beta-carboline alkaloids present in Harmala seed (syrian rue, although I do not believe Peganum harmala itself contains THH, only harmine, harmaline and a bunch of quinazoline alkaloids totally unrelated to the beta-carboline MAOIs), and the yage vine (Banisteriopsis caapi, which DOES contain THH), coptisine may well be toxic,
Chelerythrine and berberine are present also, chelerythrine is, according to wikipedia, had to look that one up, a very potent protein kinase-C inhibitor, which could have effects all over the show, as PKCs are a large family of enzymes with a lot of different functions, I don't know what the effects of nonselective, large-scale inhibition of a whole bunch of PKC isoforms and subtypes would have, but I doubt they would be good ones.
Berberine is not particularly toxic, and has quite interesting pharmacology, increasing the sensitivity of insulin receptors, potential anticancer agent, and also a dopamine antagonist (which receptor subtype it blocks I do not know, just off the top of my head) whilst increasing serotonin and noradrenaline release (which is potentially dangerous combined with a MAOI, possibility of severe hypertensive crisis and serotonin syndrome, which is VERY unpleasant, my girlfriend had an experience with serotonin syndrome, and suffered so much, I felt awful when I found out what she went through, she thought she was going to die at the time)
Also, likely to make stimulants, including caffeine dangerous, and serotonergic agonist/releaser drugs such as SSRIs and MDMA really dangerous, although reversible inhibitors of MAO-a are far less prone to causing a hypertensive crisis with a stimulant, although it is still most foolish to take stimulants whilst taking a MAOI-a of any sort, reversible inhibitors of MAO-a will not likely cause a 'cheese reaction' when food containing tyramine in any significant quantity is eaten, as the tyramine can compete with the MAOI to boot it out of its binding site on the enzyme (hence 'reversible' or competitive), unlike the irreversible inhibitors like phenelzine, which irreversibly inhibit monoamine oxidase and require new enzyme to be synthesized, eat some aged cheese, processed cured meat, drink red wine on those, and its an instant trip to an agonizing hell, or death if you are unlucky.
Also has some antibiotic activity apparently. Repeated chronic use of antibiotics, especially where un-needed can both wipe out the beneficial bacteria which make their home in the gut, which equates to less competition for nastier bugs, and of course, has the potential to encourage development of antibiotic-resistant nasties.
I doubt very much from a few days use, that you did any harm, or if you did, probably not serious damage that you will notice, but I strongly reccomend you flush the rest of what you have.
And considering the effects of sanguinarine in particular in causing lung damage, administering something containing it via smoking, sounds like a pretty unsafe thing to do, even taking into account the fact that there are small quantities of it in Celandine.
Giving a known pulmonary toxin causing chronic effects a direct free-access pass to the lungs...ick!, no thank you.
And for mild, short-lived sedative effects...sheesh, for a plant like this, you gotta be fucking kidding me. Alternatives for such effects as far as herbs go, are lemon balm (Melissa officianalis) tea, which tastes lovely too, and is completely benign, or valerian root, which is often stocked in many health food shops, more strongly sedating than the balm is, acts on GABAa receptors, although at a different binding site than both barbiturates, benzos, and the neurosteroid agonists, and of course GABA itself. Valerian root is stinky stuff, smells like old unwashed socks soaked in cat piss, but its quite a benign sedative, and interestingly, when I have taken it, it caused incredibly vivid dreaming, but tolerance to that effect seems to build very rapidly indeed, within a couple of days.
There is a lot of greater Celandine growing round here, not huge amounts, but its pretty common near where I live, and I have when I was younger and picked the plant, intrigued by its bright yellow sap, happened to get it on my skin, and it was very irritating stuff.
No way in hell would I actually EAT any, and less still smoke the stuff...fuck no, whilst its effects are not as acutely disabling (short of actual serious acute toxicity if one were to ingest a large quantity of this) I would categorize this plant as right next to belladonna and Daturas in terms of its 'fuck that right off' acceptability, wouldn't touch it with somebody else's third-hand ten foot shitty stick.
D).