Starvation mode mostly applies to those people who say that they have a goal of eating fewer than 1000 calories per day or something like that. Or who plan to eat only one meal a day. Or who are going to do soemthing like a 10 day juice fast. Anything that puts your body below the number of calories it needs to survive for a lengthy amount of time is going to put you in "starvation mode" (or what I prefer to refer to as "survival mode").
OTOH, you can have an occassional day of extremely low calories and it's not going to make your body freak out. For example, last week I was ill with a tummy virus. I guarantee you that on Tues and Wed of last week I consumed 400 calories at the MOST. And those calories I did consume, I promptly threw up again (yuck)!
I don't think that 2 days of being ill and eating absolutely nothing put me into survival mode. I do think if I ate only 700 calories a day for 2 weeks, that my body would rebel and start hanging on to anything and everything I gave it.
FWIW, in my journey, I've set myself a range of 1300 - 1500 calories a day. I aim for the 1300 number and that gives me some padding if I underestimate or find myself in a situation where I want a snack or a drink. It allows me a glass of wine on a stressful day or a couple of squares of chocolate as a treat, if I want!
And I've lost 60+ lbs over a period of about a year, with 30 more to go.