Point#1. Those who hate rasool(s.a.w.) do not care for any real evidence. They try to make things sound professional and hope it effects us. Such PATHETIC attempts can only have effect on those who are dwindling in their faith(may allah swt make all muslims faith strong).
Point#2. Yes there is an enourmous difference between saddness and suicidal tendencies. Saddness is a common emotion that every human shares. Suicidal tendencies fall into the criteria of SEVERE DEPRESSION. But the claim isn't just suicidal tendencies but on top of that the attempts, which CLEARLY cannot be defined by just mere saddness.
Point#3. It is possible that the through time the understanding of that hadith might have changed, where since rophet muhammad pbuh went to the top, some people might have thought it might be a suicide attempt but clearly there is no real evidence to state this, most of these are just conjectures.
Last Point. Which may also be the most important point, in the quranic verse NOTE that there is NO MENTION of prophet muhammad pbuh trying any suicidal attempt, but rather mentioned only 2 factors: "your Lord has NOT FORSAKEN you, NOR is DISPLEASED with you."
Why is there no mention of any sort of the suicidal attempt which these mushrikeen claim? I rest my case.
Also it seems these mushrikeen who like to attack prophet muhammad pbuh glorious character are head and heels in trying so hard to find something that can stick, lets just hope that they do not end up having SUICIDAL TENDENCIES, but rather come to islam in love for allah swt and muhammad pbuh. =)