What is the meaning of "sesh"?

What's "pair up" mean and when's it used?

Here, "pair up" means to connect one device to another, usually through a Bluetooth connection. "Pair up" can also mean for people to get into a group of two, as "pair" means "two." Ex: I paired my phone up to the speaker, but the music isn't playing. Ex: Pair up! You'll be doing a project with a partner this semester.

When can I use the expression "big day"?

"Big day" is an expression used to indicate that something important or significant will be happening that day. This can refer to both positive or negative things. Ex: It's a big day for me today. I'll be taking my university entrance exams. Ex: It'll be a big day tomorrow, so go to sleep early and get some rest.

What does “be about to” mean?

"Be about to" means to start to do something; to start an action. Here are a couple of examples: Ex: I was about to bake a cake until my children interrupted me. Ex: They were about to go but then they got a flat tire. Thank you so much for your question! Feel free to ask any questions that you would like :)

Can I say "don't be so surprised" instead?

Yes, you can. "Don't have a heart attack" can be replaced by "don't be too surprised" without changing the meaning of the sentence, although the effect of exaggeration is lessened. "Don't have a heart attack" is a casual expression that can be used to show off your fluency in English, so using it is recommended. Ex: I have a surprise for you! Don't have a heart attack. = I have something for you! Don't be too surprised.

As an adverb, what does "solemnly" mean? In what circumstances could I use it?

As an adverb, "solemnly" means with deep sincerity or in a formal manner. It's often used in legal matters when you "solemnly swear" something - to swear to say or do something with deep sincerity. Or if you're just doing something with sincerity. It can also reference official matters. Ex: He solemnly vowed to come back to the city next year to visit. Ex: She was solemnly sworn into the government office that week.