I see horrible dreams although I perform the prescribed prayers, what do you make of that?

All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.

Be mindful of Allah while awake and he will safeguard you from whatever evil you see while asleep. We advise you to make the pre-sleep supplications. And Allah The Almighty Knows Best.

Is it permissible for a woman to have her underwear on while performing Umrah?

Yes, it is permissible for a woman to have her underwear on while performing Umrah. This is because she should keep her regular clothes that cover all her body while being in a state of Ihram(ritual consecration) for Hajj, or Umrah. However, she should uncover her face and hands, but it is permissible for her to let her head-covering garment drape from her head down over her face when non-Mahram (i.e., marriageable) men pass by her.

What should a sick person, who is incapable of fasting, and who didn`t make up for missed fasting days, do?

One who has missed fasting days is obliged to make up for them, but if he/she wasn`t able to because of an incurable disease , or old age, then he/she has to pay a ransom which is feeding a needy person for each of the missed fasting days.

Is it permissible for a woman who is observing `Iddah(waiting period) due to the death of her husband to travel for performing Umrah(Minor Hajj)?

A woman observing `Iddah of a revocable(Rajee`) divorce isn`t allowed to travel for Umrah except with the consent of her husband.