If someone says they "have butterflies in their stomach," what are they most likely feeling?

• Have butterflies (in your stomach) [idiom]
English meaning: to feel very nervous, usually about something you are going to do.
Bangla meaning: (কোনো দুশ্চিন্তাহেতু) পেট মোচড়ানো; বমি বমি লাগা।

Example: 
- I had terrible butterflies before I gave that talk in Venice.

Source: Cambridge & Accessible Dictionary.