You have gotten some great info on this thread, Do check out the rest of the site Gnome linked to. You will find it very helpful.
I wouldn't be so quick to absolutely say that is the cause, There are too many other variables to be considered, {Stress due to Environmental changes, Potential over/under watering, etc.}Katharina wrote:
Now, about the "decent light"... where do I start... is there such thing us "too decent"? Coz I think this is what my poor little tree nearly died of.
Chinese elms are pretty forgiving of errors and are resilient trees- They tend to bounce back

IMO it is not likely that the blazing February Irish sunKatharina wrote:
I kept it at the window, as suggested in the brochure. The only thing is that the window faces east and in the morning it can get realy hot over there. At this stage I even suspect that I didn't just dry my happy tree out. I think I might have burnt it... Is it possible?

This was most likely a combination of other factors, Including the care it received before you got it.
I agree with this entirely, Four days is a blink of an eye time-wise to a tree. I am betting it is in a fairly moisture retentive soil as well. [Which could be part of the problem.]Randy wrote: I wouldn't give up on the plant. I doubt going 4 days without water will kill it unless it was outdoors in brutally hot windy weather.
It is important to check each day as Randy stated.
His system for determining if you need to water is a good one, But [like any]is effective only if you apply it..

Again only water as it is required by the tree.
Post some pictures please if your able. [url=https://www.helpfulgardener.com/forum/viewtopic.php?t=3557]Photo tips[/url]
Good luck and please keep us posted.
ynot