Theory:

     There was panic everywhere. An old lady prayed aloud, “Oh God! Have mercy on us. My only son is waiting for me in Singapore.”
 
     A gentleman consoled her, “Don’t worry, Madam, it’s only a warning. We may not be affected at all.”
 
     Another lady, who was sitting beside me, looked very ill. “Not rough weather! I’m  already seasick. A rough sea will be the end of me!”
Explanation:
 
Despite the captain's request that the passengers not be worried, things were getting worse. The danger of the sea frightened people. "Oh, God! Have mercy on us", called out an old woman, pleading for God to save the passengers from the impending disaster. She prayed to God to save the ship as her only son was waiting in Singapore for her arrival.
 
On seeing her being anxious and worry, a gentleman comforted her with his soothing words. He told her that nothing would harm her because the Captain's announcement was just a warning. He tried to console her, explaining that there were fewer chances for the ship to meet with a disaster since the announcement wasn't severe. Another woman seated next to Vasantha seemed to be very sick. She was extremely worried, and she confirmed that she was already seasick. So, if the reported announcement would come true, she would undoubtedly pass away with the action of a rough sea.
 
Meaning of difficult words:
  
S. No.
Words
Meaning
1.
Console
To try to make someone feeling better
2.
Disaster
An event that causes lot of harm or damage
3.
Beside
Next to or at the side of somebody or something
Reference:
State Council of Educational Research and Training (2018). Term-3 English Standard-7. Man Overboard - Vasantha Murthi (pp. 125-130). Published by the Tamil Nadu Textbook and Educational Services Corporation.