What is the meaning of "Lema'an Yachseru"?
Rashi: Their worry and frenzy is because they will lack bread and water during the siege, and they worry lest it finish.
Malbim: Hashem told Yechezkel that after 390 days, his bread will be reduced from this weight (20 Shekalim). This is a sign that they will lack bread and water 40 days before the city is breached.
What is the meaning of "v'Nashamu Ish v'Achiv"?
Radak: All will be astounded. No one will be better (calmer) than his colleague.
Malbim: There will be tumults and wars between people, for some wanted to cleave the city. Then they will melt via plague, sword and hunger - "Hineni Mesev Es Klei ha'Milchamah Asher b'Yedchem" (Yirmeyah 21:4).
How will they melt?
Radak: Their hearts will melt amidst great afflictions. They will recognize that they caused all this via their sins.