Switching Between Languages

If you speak at least three languages, I hope that you'll add your comments here. On another site, a woman wrote that she had trouble switching between languages and even thought it "bad" or "unhealthy" to switch between multiple languages.

I think this is an unusual opinion to say the least.

When I switch between languages quickly, I think my pulse rate probably increases. There is the potential for an adrenaline rush along with the accompanying symptoms, but I don't see this as harmful unless the person is so nervous as to have anxiety.

I can switch between certain languages easily, but others not so well.
For example it is easy for me to switch between my native language and any other language I speak, but less easy for me to switch between Japanese and French (on the spot interpreting, I mean, not reading, or leisurely conversation).

What experiences have you had with this?

I'm speak Portuguese, French and English and can switch easily between them. Then again I live in Montreal, a bilingual city, and learned French and English at a very young age from TV and school and learned Portuguese from my parents and Portuguese school.

Because of this even though Portuguese is the first language I learned to speak, I feel like I don't really have a native language/mother tongue.

That's interesting. I've noticed that people who are trilingual from early childhood tend to learn languages well.

I speak Spanish (second lang.), French (third lang.) , English (native language), Portuguese (fourth lang.), and Mandarin Chinese (fifth lang.). I don't really find it difficult to switch between most of the languages. I will say, however, that switching between Mandarin Chinese and the others is more difficult. And then again I only speak Mandarin Chinese at an intermediate level. The others I speak fluently. I don't know. What do you think?